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Move array elements to another array in Ruby

A simple ruby ​​question. Let's say I have an array of 10 strings and I want to move the elements in array [3] and array [5] into a completely new array. The new array will only have two elements that I moved from the first array. And the first array will only have 8 elements since two of them have been moved.

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5 answers


Use Array#slice!

to remove elements from the first array and add them to the second array with Array#<<

:

arr1 = ['Foo', 'Bar', 'Baz', 'Qux']
arr2 = []

arr2 << arr1.slice!(1)
arr2 << arr1.slice!(2)

puts arr1.inspect
puts arr2.inspect

Output:

["Foo", "Baz"]
["Bar", "Qux"]


Depending on your specific situation, you may find other methods on the array even more useful, for example Enumerable#partition

:

arr = ['Foo', 'Bar', 'Baz', 'Qux']
starts_with_b, does_not_start_with_b = arr.partition{|word| word[0] == 'B'}

puts starts_with_b.inspect
puts does_not_start_with_b.inspect

Output:

["Bar", "Baz"]
["Foo", "Qux"]
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a = (0..9).map { |i| "el##{i}" }
x = [3, 5].sort_by { |i| -i }.map { |i| a.delete_at(i) }
puts x.inspect
# => ["el#5", "el#3"]
puts a.inspect
# => ["el#0", "el#1", "el#2", "el#4", "el#6", "el#7", "el#8", "el#9"]


As noted in the comments, there is some magic to keep the indexes in place. This can be avoided by first getting all the items you want with a.values_at(*indices)

, then deleting them as above.

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Code:

arr = ["null","one","two","three","four","five","six","seven","eight","nine"]

p "Array: #{arr}"

third_el = arr.delete_at(3)
fifth_el = arr.delete_at(4)
first_arr = arr
p "First array: #{first_arr}"

concat_el = third_el + "," + fifth_el
second_arr = concat_el.split(",")
p "Second array: #{second_arr}"

Output:

c:\temp>C:\case.rb
"Array: [\"null\", \"one\", \"two\", \"three\", \"four\", \"five\", \"six\", \"s
even\", \"eight\", \"nine\"]"
"First array: [\"null\", \"one\", \"two\", \"four\", \"six\", \"seven\", \"eight
\", \"nine\"]"
"Second array: [\"three\", \"five\"]"
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Here's one way:

vals  = arr.values_at *pulls
arr   = arr.values_at *([*(0...arr.size)] - pulls)

Try it.

arr   = %w[Now is the time for all Rubyists to code]
pulls = [3,5]

vals  = arr.values_at *pulls
  #=>     ["time", "all"]
arr   = arr.values_at *([*(0...arr.size)] - pulls)
  #=>     ["Now", "is", "the", "for", "Rubyists", "to", "code"]

arr   = %w[Now is the time for all Rubyists to code]
pulls = [5,3]

vals  = arr.values_at *pulls
  #=>     ["all", "time"]
arr   = arr.values_at *([*(0...arr.size)] - pulls)
  #=>     ["Now", "is", "the", "for", "Rubyists", "to", "code"]
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Why not start deleting from the index as much as possible .

arr = ['Foo', 'Bar', 'Baz', 'Qux']
index_array = [2, 1]
new_ary = index_array.map { |index| arr.delete_at(index) }
new_ary # => ["Baz", "Bar"]
arr # => ["Foo", "Qux"]
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