How to return a part of an array in Ruby

Question

With a list in Python I can return a part of it using the following code   foo    1 2 3 4 5 6  bar    10 20 30 40 50 60  half   len foo    2 foobar   foo  half    bar half     Since Ruby does everything in arrays I wonder if there is something similar to that

User · Answer

Ruby 2 6 Beginless Endless Ranges     1    or     1           1      or  1           1 2 3 4 5 6    3    gt   1  2  3  4    1 2 3 4 5 6     3     gt   1  2  3         ROLES    w superadmin manager admin contact user  ROLES ROLES index  admin        gt    admin    contact    user

User · Answer

Yes  Ruby has very similar array-slicing syntax to Python  Here is the ri documentation for the array index method   --------------------------------------------------------------- Array         array index                 - gt  obj      or nil      array start  length         - gt  an array or nil      array range                 - gt  an array or nil      array slice index           - gt  obj      or nil      array slice start  length   - gt  an array or nil      array slice range           - gt  an array or nil ------------------------------------------------------------------------      Element Reference---Returns the element at index  or returns a       subarray starting at start and continuing for length elements  or       returns a subarray specified by range  Negative indices count       backward from the end of the array  -1 is the last element         Returns nil if the index  or starting index  are out of range           a      a    b    c    d    e            a 2     a 0    a 1        gt   cab          a 6                       gt  nil         a 1  2                    gt     b    c            a 1  3                    gt     b    c    d            a 4  7                    gt     e            a 6  10                   gt  nil         a -3  3                   gt     c    d    e              special cases         a 5                       gt  nil         a 6  1                    gt  nil         a 5  1                    gt             a 5  10                   gt

User · Answer

I like ranges for this   def first half list    list 0    list length   2   end  def last half list    list  list length   2   list length  end   However  be very careful about whether the endpoint is included in your range  This becomes critical on an odd-length list where you need to choose where you re going to break the middle  Otherwise you ll end up double-counting the middle element   The above example will consistently put the middle element in the last half

User · Answer

another way is to use the range method  foo    1 2 3 4 5 6  bar    10 20 30 40 50 60  a   foo 0   3  b   bar 3   6   print a   b    gt   1  2  3  40  50   60

User · Answer

You can use slice   for this    gt  gt  foo    1 2 3 4 5 6    gt   1  2  3  4  5  6   gt  gt  bar    10 20 30 40 50 60    gt   10  20  30  40  50  60   gt  gt  half   foo length   2   gt  3  gt  gt  foobar   foo slice 0  half    bar slice half  foo length    gt   1  2  3  40  50  60    By the way  to the best of my knowledge  Python  lists  are just efficiently implemented dynamically growing arrays   Insertion at the beginning is in O n   insertion at the end is amortized O 1   random access is O 1

User · Answer

If you want to split cut the array on an index i   arr   arr drop i    gt  arr    1 2 3 4 5     gt   1  2  3  4  5    gt  arr drop 2     gt   3  4  5

[ruby] How to return a part of an array in Ruby?

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