What is the right way to iterate through an array in Ruby

Question

PHP  for all its warts  is pretty good on this count  There s no difference between an array and a hash  maybe I m naive  but this seems obviously right to me   and to iterate through either you just do  foreach  array hash as  key   gt   value    In Ruby there are a bunch of ways to do this sort of thing   array length times do  i  end  array each  array each index  for i in array   Hashes make more sense  since I just always use  hash each do  key  value    Why can t I do this for arrays  If I want to remember just one method  I guess I can use each index  since it makes both the index and value available   but it s annoying to have to do array index  instead of just value     Oh right  I forgot about array each with index  However  this one sucks because it goes  value  key  and hash each goes  key  value   Is this not insane

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In Ruby 2 1  each with index method is removed  Instead you can use each index  Example   a      a    b    c    a each index   x  print x    --       produces   0 -- 1 -- 2 --

User · Answer

If you use the enumerable mixin  as Rails does  you can do something similar to the php snippet listed  Just use the each slice method and flatten the hash   require  enumerator      a  1  b  2  to a flatten each slice 2    x y  puts    x    gt    y        is equivalent to       a   gt 1  b   gt 2  to a flatten each slice 2    x y  puts    x    gt    y       Less monkey-patching required   However  this does cause problems when you have a recursive array or a hash with array values  In ruby 1 9 this problem is solved with a parameter to the flatten method that specifies how deep to recurse     Ruby 1 8  1 2  1 2 3   flatten   gt   1 2 1 2 3     Ruby 1 9  1 2  1 2 3   flatten 0    gt   1 2  1 2 3     As for the question of whether this is a code smell  I m not sure  Usually when I have to bend over backwards to iterate over something I step back and realize I m attacking the problem wrong

User · Answer

Use each with index when you need both   ary each with index    val  idx

User · Answer

The right way is the one you feel most comfortable with and which does what you want it to do  In programming there is rarely one  correct  way to do things  more often there are multiple ways to choose    If you are comfortable with certain way of doings things  do just it  unless it doesn t work - then it is time to find better way

User · Answer

Use each with index when you need both   ary each with index    val  idx

User · Answer

I d been trying to build a menu  in Camping and Markaby  using a hash   Each item has 2 elements  a menu label and a URL  so a hash seemed right  but the     URL for  Home  always appeared last  as you d expect for a hash   so menu items appeared in the wrong order   Using an array with each slice does the job     Home         Page two    two    Test    test   each slice 2  do label link     li  a label   href   gt  link  end   Adding extra values for each menu item  e g  like a CSS ID name  just means increasing the slice value  So  like a hash but with groups consisting of any number of items  Perfect   So this is just to say thanks for inadvertently hinting at a solution   Obvious  but worth stating  I suggest checking if the length of the array is divisible by the slice value

User · Answer

I think there is no one right way   There are a lot of different ways to iterate  and each has its own niche    each is sufficient for many usages  since I don t often care about the indexes    each  with  index acts like Hash each - you get the value and the index  each index - just the indexes   I don t use this one often  Equivalent to  length times   map is another way to iterate  useful when you want to transform one array into another  select is the iterator to use when you want to choose a subset  inject is useful for generating sums or products  or collecting a single result     It may seem like a lot to remember  but don t worry  you can get by without knowing all of them   But as you start to learn and use the different methods  your code will become cleaner and clearer  and you ll be on your way to Ruby mastery

User · Answer

Use each with index when you need both   ary each with index    val  idx

User · Answer

Trying to do the same thing consistently with arrays and hashes might just be a code smell  but  at the risk of my being branded as a codorous half-monkey-patcher  if you re looking for consistent behaviour  would this do the trick    class Hash     def each pairwise         self each     x  y               yield  x  y                end end  class Array     def each pairwise         self each with index     x  y               yield  y  x                end end    a   b   c   each pairwise    x y      puts    x    gt    y        a    gt   Aardvark   b    gt   Bogle   c    gt   Catastrophe   each pairwise    x y      puts    x    gt    y

User · Answer

If you use the enumerable mixin  as Rails does  you can do something similar to the php snippet listed  Just use the each slice method and flatten the hash   require  enumerator      a  1  b  2  to a flatten each slice 2    x y  puts    x    gt    y        is equivalent to       a   gt 1  b   gt 2  to a flatten each slice 2    x y  puts    x    gt    y       Less monkey-patching required   However  this does cause problems when you have a recursive array or a hash with array values  In ruby 1 9 this problem is solved with a parameter to the flatten method that specifies how deep to recurse     Ruby 1 8  1 2  1 2 3   flatten   gt   1 2 1 2 3     Ruby 1 9  1 2  1 2 3   flatten 0    gt   1 2  1 2 3     As for the question of whether this is a code smell  I m not sure  Usually when I have to bend over backwards to iterate over something I step back and realize I m attacking the problem wrong

User · Answer

I think there is no one right way   There are a lot of different ways to iterate  and each has its own niche    each is sufficient for many usages  since I don t often care about the indexes    each  with  index acts like Hash each - you get the value and the index  each index - just the indexes   I don t use this one often  Equivalent to  length times   map is another way to iterate  useful when you want to transform one array into another  select is the iterator to use when you want to choose a subset  inject is useful for generating sums or products  or collecting a single result     It may seem like a lot to remember  but don t worry  you can get by without knowing all of them   But as you start to learn and use the different methods  your code will become cleaner and clearer  and you ll be on your way to Ruby mastery

User · Answer

I m not saying that Array -   value index  and Hash -   key value  is not insane  see Horace Loeb s comment   but I am saying that there is a sane way to expect this arrangement   When I am dealing with arrays  I am focused on the elements in the array  not the index because the index is transitory    The method is each with index  i e  each index  or  each index   or  value index    This is also consistent with the index being viewed as an optional argument  e g   value  is equivalent to  value index nil  which is consistent with  value index    When I am dealing with hashes  I am often more focused on the keys than the values  and I am usually dealing with keys and values in that order  either key   gt  value or hash key    value   If you want duck-typing  then either explicitly use a defined method as Brent Longborough showed  or an implicit method as maxhawkins showed   Ruby is all about accommodating the language to suit the programmer  not about the programmer accommodating to suit the language   This is why there are so many ways   There are so many ways to think about something   In Ruby  you choose the closest and the rest of the code usually falls out extremely neatly and concisely   As for the original question   What is the    right    way to iterate through an array in Ruby    well  I think the core way  i e  without powerful syntactic sugar or object oriented power  is to do   for index in 0     array size   puts  array   index       array index  inspect   end   But Ruby is all about powerful syntactic sugar and object oriented power  but anyway here is the equivalent for hashes  and the keys can be ordered or not   for key in hash keys sort   puts  hash   key inspect       hash key  inspect   end   So  my answer is   The    right    way to iterate through an array in Ruby depends on you  i e  the programmer or the programming team  and the project     The better Ruby programmer makes the better choice  of which syntactic power and or which object oriented approach    The better Ruby programmer continues to look for more ways     Now  I want to ask another question   What is the    right    way to iterate through a Range in Ruby backwards      This question is how I came to this page    It is nice to do  for the forwards     1  10  each  i  puts  i   i       but I don t like to do  for the backwards     1  10  to a reverse each  i  puts  i   i       Well  I don t actually mind doing that too much  but when I am teaching going backwards  I want to show my students a nice symmetry  i e  with minimal difference  e g  only adding a reverse  or a step -1  but without modifying anything else   You can do  for symmetry     a  1  10  each  i  puts  i   i       and   a  1  10  reverse each  i  puts  i   i       which I don t like much  but you can t do    1  10  each  i  puts  i   i       1  10  reverse each  i  puts  i   i        1  10  step 1   i  puts  i   i      1  10  step -1   i  puts  i   i        1  10  each  i  puts  i   i      10  1  each  i  puts  i   i         I don t want this though   It s dangerous   You could ultimately do  class Range    def each reverse  amp block      self to a reverse each  amp block    end  end   but I want to teach pure Ruby rather than object oriented approaches  just yet    I would like to iterate backwards    without creating an array  consider 0  1000000000  working for any Range  e g  Strings  not just Integers  without using any extra object oriented power  i e  no class modification    I believe this is impossible without defining a pred method  which means modifying the Range class to use it   If you can do this please let me know  otherwise confirmation of impossibility would be appreciated though it would be disappointing   Perhaps Ruby 1 9 addresses this    Thanks for your time in reading this

User · Answer

I d been trying to build a menu  in Camping and Markaby  using a hash   Each item has 2 elements  a menu label and a URL  so a hash seemed right  but the     URL for  Home  always appeared last  as you d expect for a hash   so menu items appeared in the wrong order   Using an array with each slice does the job     Home         Page two    two    Test    test   each slice 2  do label link     li  a label   href   gt  link  end   Adding extra values for each menu item  e g  like a CSS ID name  just means increasing the slice value  So  like a hash but with groups consisting of any number of items  Perfect   So this is just to say thanks for inadvertently hinting at a solution   Obvious  but worth stating  I suggest checking if the length of the array is divisible by the slice value

User · Answer

Trying to do the same thing consistently with arrays and hashes might just be a code smell  but  at the risk of my being branded as a codorous half-monkey-patcher  if you re looking for consistent behaviour  would this do the trick    class Hash     def each pairwise         self each     x  y               yield  x  y                end end  class Array     def each pairwise         self each with index     x  y               yield  y  x                end end    a   b   c   each pairwise    x y      puts    x    gt    y        a    gt   Aardvark   b    gt   Bogle   c    gt   Catastrophe   each pairwise    x y      puts    x    gt    y

User · Answer

If you use the enumerable mixin  as Rails does  you can do something similar to the php snippet listed  Just use the each slice method and flatten the hash   require  enumerator      a  1  b  2  to a flatten each slice 2    x y  puts    x    gt    y        is equivalent to       a   gt 1  b   gt 2  to a flatten each slice 2    x y  puts    x    gt    y       Less monkey-patching required   However  this does cause problems when you have a recursive array or a hash with array values  In ruby 1 9 this problem is solved with a parameter to the flatten method that specifies how deep to recurse     Ruby 1 8  1 2  1 2 3   flatten   gt   1 2 1 2 3     Ruby 1 9  1 2  1 2 3   flatten 0    gt   1 2  1 2 3     As for the question of whether this is a code smell  I m not sure  Usually when I have to bend over backwards to iterate over something I step back and realize I m attacking the problem wrong

User · Answer

In Ruby 2 1  each with index method is removed  Instead you can use each index  Example   a      a    b    c    a each index   x  print x    --       produces   0 -- 1 -- 2 --

User · Answer

This will iterate through all the elements   array    1  2  3  4  5  6  array each    x  puts x     Prints   1 2 3 4 5 6   This will iterate through all the elements giving you the value and the index   array     A    B    C   array each with index   val  index  puts    val    gt    index       Prints   A   gt  0 B   gt  1 C   gt  2   I m not quite sure from your question which one you are looking for

User · Answer

Here are the four options listed in your question  arranged by freedom of control  You might want to use a different one depending on what you need    Simply go through values   array each  Simply go through indices   array each index  Go through indices   index variable   for i in array  Control loop count   index variable   array length times do   i

User · Answer

I m not saying that Array -   value index  and Hash -   key value  is not insane  see Horace Loeb s comment   but I am saying that there is a sane way to expect this arrangement   When I am dealing with arrays  I am focused on the elements in the array  not the index because the index is transitory    The method is each with index  i e  each index  or  each index   or  value index    This is also consistent with the index being viewed as an optional argument  e g   value  is equivalent to  value index nil  which is consistent with  value index    When I am dealing with hashes  I am often more focused on the keys than the values  and I am usually dealing with keys and values in that order  either key   gt  value or hash key    value   If you want duck-typing  then either explicitly use a defined method as Brent Longborough showed  or an implicit method as maxhawkins showed   Ruby is all about accommodating the language to suit the programmer  not about the programmer accommodating to suit the language   This is why there are so many ways   There are so many ways to think about something   In Ruby  you choose the closest and the rest of the code usually falls out extremely neatly and concisely   As for the original question   What is the    right    way to iterate through an array in Ruby    well  I think the core way  i e  without powerful syntactic sugar or object oriented power  is to do   for index in 0     array size   puts  array   index       array index  inspect   end   But Ruby is all about powerful syntactic sugar and object oriented power  but anyway here is the equivalent for hashes  and the keys can be ordered or not   for key in hash keys sort   puts  hash   key inspect       hash key  inspect   end   So  my answer is   The    right    way to iterate through an array in Ruby depends on you  i e  the programmer or the programming team  and the project     The better Ruby programmer makes the better choice  of which syntactic power and or which object oriented approach    The better Ruby programmer continues to look for more ways     Now  I want to ask another question   What is the    right    way to iterate through a Range in Ruby backwards      This question is how I came to this page    It is nice to do  for the forwards     1  10  each  i  puts  i   i       but I don t like to do  for the backwards     1  10  to a reverse each  i  puts  i   i       Well  I don t actually mind doing that too much  but when I am teaching going backwards  I want to show my students a nice symmetry  i e  with minimal difference  e g  only adding a reverse  or a step -1  but without modifying anything else   You can do  for symmetry     a  1  10  each  i  puts  i   i       and   a  1  10  reverse each  i  puts  i   i       which I don t like much  but you can t do    1  10  each  i  puts  i   i       1  10  reverse each  i  puts  i   i        1  10  step 1   i  puts  i   i      1  10  step -1   i  puts  i   i        1  10  each  i  puts  i   i      10  1  each  i  puts  i   i         I don t want this though   It s dangerous   You could ultimately do  class Range    def each reverse  amp block      self to a reverse each  amp block    end  end   but I want to teach pure Ruby rather than object oriented approaches  just yet    I would like to iterate backwards    without creating an array  consider 0  1000000000  working for any Range  e g  Strings  not just Integers  without using any extra object oriented power  i e  no class modification    I believe this is impossible without defining a pred method  which means modifying the Range class to use it   If you can do this please let me know  otherwise confirmation of impossibility would be appreciated though it would be disappointing   Perhaps Ruby 1 9 addresses this    Thanks for your time in reading this

User · Answer

Using the same method for iterating through both arrays and hashes makes sense  for example to process nested hash-and-array structures often resulting from parsers  from reading JSON files etc    One clever way that has not yet been mentioned is how it s done in the Ruby Facets library of standard library extensions  From here   class Array      Iterate over index and value  The intention of this     method is to provide polymorphism with Hash        def each pair   yield      each with index   e  i  yield i e      end  end   There is already Hash each pair  an alias of Hash each  So after this patch  we also have Array each pair and can use it interchangeably to iterate through both Hashes and Arrays  This fixes the OP s observed insanity that Array each with index has the block arguments reversed compared to Hash each  Example usage   my array     Hello    World        my array each pair    key  value  pp    key     value        result    0  Hello   1  World   2      my hash      0    gt   Hello    1    gt   World    2    gt        my hash each pair    key  value  pp    key     value        result    0  Hello   1  World   2

User · Answer

Here are the four options listed in your question  arranged by freedom of control  You might want to use a different one depending on what you need    Simply go through values   array each  Simply go through indices   array each index  Go through indices   index variable   for i in array  Control loop count   index variable   array length times do   i

User · Answer

This will iterate through all the elements   array    1  2  3  4  5  6  array each    x  puts x     Prints   1 2 3 4 5 6   This will iterate through all the elements giving you the value and the index   array     A    B    C   array each with index   val  index  puts    val    gt    index       Prints   A   gt  0 B   gt  1 C   gt  2   I m not quite sure from your question which one you are looking for

User · Answer

Trying to do the same thing consistently with arrays and hashes might just be a code smell  but  at the risk of my being branded as a codorous half-monkey-patcher  if you re looking for consistent behaviour  would this do the trick    class Hash     def each pairwise         self each     x  y               yield  x  y                end end  class Array     def each pairwise         self each with index     x  y               yield  y  x                end end    a   b   c   each pairwise    x y      puts    x    gt    y        a    gt   Aardvark   b    gt   Bogle   c    gt   Catastrophe   each pairwise    x y      puts    x    gt    y

User · Answer

If you use the enumerable mixin  as Rails does  you can do something similar to the php snippet listed  Just use the each slice method and flatten the hash   require  enumerator      a  1  b  2  to a flatten each slice 2    x y  puts    x    gt    y        is equivalent to       a   gt 1  b   gt 2  to a flatten each slice 2    x y  puts    x    gt    y       Less monkey-patching required   However  this does cause problems when you have a recursive array or a hash with array values  In ruby 1 9 this problem is solved with a parameter to the flatten method that specifies how deep to recurse     Ruby 1 8  1 2  1 2 3   flatten   gt   1 2 1 2 3     Ruby 1 9  1 2  1 2 3   flatten 0    gt   1 2  1 2 3     As for the question of whether this is a code smell  I m not sure  Usually when I have to bend over backwards to iterate over something I step back and realize I m attacking the problem wrong

User · Answer

I think there is no one right way   There are a lot of different ways to iterate  and each has its own niche    each is sufficient for many usages  since I don t often care about the indexes    each  with  index acts like Hash each - you get the value and the index  each index - just the indexes   I don t use this one often  Equivalent to  length times   map is another way to iterate  useful when you want to transform one array into another  select is the iterator to use when you want to choose a subset  inject is useful for generating sums or products  or collecting a single result     It may seem like a lot to remember  but don t worry  you can get by without knowing all of them   But as you start to learn and use the different methods  your code will become cleaner and clearer  and you ll be on your way to Ruby mastery

User · Answer

The other answers are just fine  but I wanted to point out one other peripheral thing  Arrays are ordered  whereas Hashes are not in 1 8    In Ruby 1 9  Hashes are ordered by insertion order of keys    So it wouldn t make sense prior to 1 9 to iterate over a Hash in the same way sequence as Arrays  which have always had a definite ordering   I don t know what the default order is for PHP associative arrays  apparently my google fu isn t strong enough to figure that out  either   but I don t know how you can consider regular PHP arrays and PHP associative arrays to be  the same  in this context  since the order for associative arrays seems undefined   As such  the Ruby way seems more clear and intuitive to me

User · Answer

Using the same method for iterating through both arrays and hashes makes sense  for example to process nested hash-and-array structures often resulting from parsers  from reading JSON files etc    One clever way that has not yet been mentioned is how it s done in the Ruby Facets library of standard library extensions  From here   class Array      Iterate over index and value  The intention of this     method is to provide polymorphism with Hash        def each pair   yield      each with index   e  i  yield i e      end  end   There is already Hash each pair  an alias of Hash each  So after this patch  we also have Array each pair and can use it interchangeably to iterate through both Hashes and Arrays  This fixes the OP s observed insanity that Array each with index has the block arguments reversed compared to Hash each  Example usage   my array     Hello    World        my array each pair    key  value  pp    key     value        result    0  Hello   1  World   2      my hash      0    gt   Hello    1    gt   World    2    gt        my hash each pair    key  value  pp    key     value        result    0  Hello   1  World   2

User · Answer

I think there is no one right way   There are a lot of different ways to iterate  and each has its own niche    each is sufficient for many usages  since I don t often care about the indexes    each  with  index acts like Hash each - you get the value and the index  each index - just the indexes   I don t use this one often  Equivalent to  length times   map is another way to iterate  useful when you want to transform one array into another  select is the iterator to use when you want to choose a subset  inject is useful for generating sums or products  or collecting a single result     It may seem like a lot to remember  but don t worry  you can get by without knowing all of them   But as you start to learn and use the different methods  your code will become cleaner and clearer  and you ll be on your way to Ruby mastery

User · Answer

The right way is the one you feel most comfortable with and which does what you want it to do  In programming there is rarely one  correct  way to do things  more often there are multiple ways to choose    If you are comfortable with certain way of doings things  do just it  unless it doesn t work - then it is time to find better way

User · Answer

The other answers are just fine  but I wanted to point out one other peripheral thing  Arrays are ordered  whereas Hashes are not in 1 8    In Ruby 1 9  Hashes are ordered by insertion order of keys    So it wouldn t make sense prior to 1 9 to iterate over a Hash in the same way sequence as Arrays  which have always had a definite ordering   I don t know what the default order is for PHP associative arrays  apparently my google fu isn t strong enough to figure that out  either   but I don t know how you can consider regular PHP arrays and PHP associative arrays to be  the same  in this context  since the order for associative arrays seems undefined   As such  the Ruby way seems more clear and intuitive to me

User · Answer

Trying to do the same thing consistently with arrays and hashes might just be a code smell  but  at the risk of my being branded as a codorous half-monkey-patcher  if you re looking for consistent behaviour  would this do the trick    class Hash     def each pairwise         self each     x  y               yield  x  y                end end  class Array     def each pairwise         self each with index     x  y               yield  y  x                end end    a   b   c   each pairwise    x y      puts    x    gt    y        a    gt   Aardvark   b    gt   Bogle   c    gt   Catastrophe   each pairwise    x y      puts    x    gt    y

User · Answer

The other answers are just fine  but I wanted to point out one other peripheral thing  Arrays are ordered  whereas Hashes are not in 1 8    In Ruby 1 9  Hashes are ordered by insertion order of keys    So it wouldn t make sense prior to 1 9 to iterate over a Hash in the same way sequence as Arrays  which have always had a definite ordering   I don t know what the default order is for PHP associative arrays  apparently my google fu isn t strong enough to figure that out  either   but I don t know how you can consider regular PHP arrays and PHP associative arrays to be  the same  in this context  since the order for associative arrays seems undefined   As such  the Ruby way seems more clear and intuitive to me

User · Answer

This will iterate through all the elements   array    1  2  3  4  5  6  array each    x  puts x     Prints   1 2 3 4 5 6   This will iterate through all the elements giving you the value and the index   array     A    B    C   array each with index   val  index  puts    val    gt    index       Prints   A   gt  0 B   gt  1 C   gt  2   I m not quite sure from your question which one you are looking for

User · Answer

This will iterate through all the elements   array    1  2  3  4  5  6  array each    x  puts x     Prints   1 2 3 4 5 6   This will iterate through all the elements giving you the value and the index   array     A    B    C   array each with index   val  index  puts    val    gt    index       Prints   A   gt  0 B   gt  1 C   gt  2   I m not quite sure from your question which one you are looking for

User · Answer

Use each with index when you need both   ary each with index    val  idx

User · Answer

The other answers are just fine  but I wanted to point out one other peripheral thing  Arrays are ordered  whereas Hashes are not in 1 8    In Ruby 1 9  Hashes are ordered by insertion order of keys    So it wouldn t make sense prior to 1 9 to iterate over a Hash in the same way sequence as Arrays  which have always had a definite ordering   I don t know what the default order is for PHP associative arrays  apparently my google fu isn t strong enough to figure that out  either   but I don t know how you can consider regular PHP arrays and PHP associative arrays to be  the same  in this context  since the order for associative arrays seems undefined   As such  the Ruby way seems more clear and intuitive to me

[ruby] What is the "right" way to iterate through an array in Ruby?

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