How can I delete one element from an array by value

Question

I have an array of elements in Ruby   2 4 6 3 8    I need to remove  elements with value 3 for example  How do I do that

User · Answer

Assuming you want to delete 3 by value at multiple places in an array, I think the ruby way to do this task would be to use the delete_if method:

[2,4,6,3,8,3].delete_if {|x| x == 3 }

You can also use delete_if in removing elements in the scenario of 'array of arrays'.

Hope this resolves your query

User · Answer

I think I ve figured it out   a    3  2  4  6  3  8  a delete 3     gt  3 a    gt   2  4  6  8

User · Answer

Non-destructive removal of first occurrence   a    2  4  6  3  8  n   a index 3 a take n  a drop n 1

User · Answer

If you also want to make this deletion operation chainable  so you can delete some item and keep on chaining operations on the resulting array  use tap     2  4  6  3  8  tap    ary   ary delete 3    count    gt  4

User · Answer

I m not sure if anyone has stated this  but Array delete   and -  value will delete every instance of the value passed to it within the Array  In order to delete the first instance of the particular element you could do something like  arr    1 3 2 44 5  arr delete at arr index 44       gt   1 3 2 5    There could be a simpler way  I m not saying this is best practice  but it is something that should be recognized

User · Answer

You can simply run    2 4 6 3 8  delete 3

User · Answer

You can also monkey patch it  I never understood why Ruby has an except method for Hash but not for Array   class Array   def except value     value   value kind of Array    value    value      self - value   end end   Now you can do    1 3 7  436  354 nil  except 354     gt   1 3 7  436  nil    Or    1 3 7  436  354 nil  except  354  1      gt   3 7  436  nil

User · Answer

So when you have multiple occurrences of 3 and you want only to delete the first occurrence of 3  you can simply do some thing as below   arr    2  4  6  3  8  10  3  12   arr delete at arr index 3   This will modify arr as  2  4  6  8  10  3  12  where first occurrence of 3 is deleted  Returns the element deleted  In this case   gt  3

User · Answer

A  delete at 3  3 here being the position

User · Answer

I improved Niels s solution  class Array             def except  values      self - values   end     end   Now you can use   1  2  3  4  except 3  4    return  1  2   1  2  3  4  except 4       return  1  2  3

User · Answer

Here are some benchmarks   require  fruity    class Array             def rodrigo except  values      self - values   end        def niels except value     value   value kind of  Array    value    value      self - value   end end  ARY    2 4 6 3 8   compare do   soziev    a   ARY dup  a delete 3                 a     steve     a   ARY dup  a -   3                    a     barlop    a   ARY dup  a delete if   i  i    3    a     rodrigo   a   ARY dup  a rodrigo except 3               niels     a   ARY dup  a niels except 3               end     gt  gt  Running each test 4096 times  Test will take about 2 seconds     gt  gt  soziev is similar to barlop    gt  gt  barlop is faster than steve by 2x    1 0    gt  gt  steve is faster than rodrigo by 4x    1 0    gt  gt  rodrigo is similar to niels   And again with a bigger array containing lots of duplicates   class Array             def rodrigo except  values      self - values   end        def niels except value     value   value kind of  Array    value    value      self - value   end end  ARY    2 4 6 3 8    1000  compare do   soziev    a   ARY dup  a delete 3                 a     steve     a   ARY dup  a -   3                    a     barlop    a   ARY dup  a delete if   i  i    3    a     rodrigo   a   ARY dup  a rodrigo except 3               niels     a   ARY dup  a niels except 3               end     gt  gt  Running each test 16 times  Test will take about 1 second     gt  gt  steve is faster than soziev by 30 000000000000004     10 0     gt  gt  soziev is faster than barlop by 50 0     10 0     gt  gt  barlop is faster than rodrigo by 3x    0 1    gt  gt  rodrigo is similar to niels   And even bigger with more duplicates   class Array             def rodrigo except  values      self - values   end        def niels except value     value   value kind of  Array    value    value      self - value   end end  ARY    2 4 6 3 8    100 000  compare do   soziev    a   ARY dup  a delete 3                 a     steve     a   ARY dup  a -   3                    a     barlop    a   ARY dup  a delete if   i  i    3    a     rodrigo   a   ARY dup  a rodrigo except 3               niels     a   ARY dup  a niels except 3               end     gt  gt  Running each test once  Test will take about 6 seconds     gt  gt  steve is similar to soziev    gt  gt  soziev is faster than barlop by 2x    0 1    gt  gt  barlop is faster than niels by 3x    1 0    gt  gt  niels is similar to rodrigo

User · Answer

Compiling all the different options for delete in ruby     delete - Deletes matching elements by value  If more than one value matches it will remove all  If you don t care about the number of occurrence or sure about single occurrence  use this method    a    2  6  3  5  3  7  a delete 3     returns 3 puts a         return  2  6  5  7       delete at - Deletes element at given index  If you know the index use this method      continuing from the above example a delete at 2    returns 5 puts a           returns  2  6  7       delete if - Deletes every element for which block is true  This will modify the array  Array changes instantly as the block is called    b    1  2  5  4  9  10  11  b delete if   n  n  gt   10      returns  1  2  5  4  9       reject - This will return new array with the elements for which the given block is false  The ordering is maintained with this    c    1  2  5  4  9  10  11  c reject   n  n  gt   10      returns  1  2  5  4  9       reject  - same as delete if  Array may not change instantly as the block is called       If you want to delete multiple values from array  the best option is as bellow    a    2  3  7  4  6  21  13  b    7  21  a   a - b      a -  2  3  4  6  13

User · Answer

Borrowing from Travis in the comments  this is a better answer      I personally like  1  2  7  4  5  -  7  which results in   gt   1  2  4  5  from irb   I modified his answer seeing that 3 was the third element in his example array  This could lead to some confusion for those who don t realize that 3 is in position 2 in the array

User · Answer

I like the -  4  way mentioned in other answers to delete the elements whose value is 4  But there is this way   2 4 6 3 8 6  delete if    i  i    6     gt   2  4  3  8   mentioned somewhere in  quot Basic Array Operations quot   after it mentions the map function

User · Answer

Another option   a    2 4 6 3 8   a -   3    which results in    gt   2  4  6  8

[arrays] How can I delete one element from an array by value

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