How to enter data into a new array

Question

Good morning people. I'm new to Rails and I'm using google translate to post here.

I have an array, and I would like to take a certain amount of values from the array, and put them in a new array1, for example, the first 7 numbers, and then the next 7 numbers in the second array:

array = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40]
array2 = []    
array3 = []

array = [15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40]    
array2 = [1,2,3,4,5,6,7]   
array3 = [8,9,10,11,12,13,14]

How could I do this?

https://stackoverflow.com/questions/695290/how-to-return-a-part-of-an-array-in-ruby — USERNAME GOES HERE, Jun 13 '22 at 11:26
https://rubyapi.org/3.1/o/enumerable#method-i-each_cons might also be of some help. — eugen, Jun 13 '22 at 11:27
May I ask, _why_ you want to move some elements to other arrays? Depending on your use case, there might be a better solution than creating a bunch of numbered variables. — Stefan, Jun 13 '22 at 12:11

Josien · Answer 1 · 2022-06-13T12:44:46.903

You can use the Ruby shift Array method to accomplish this:

array = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40]
array2 = array.shift(7) # array2 is now [1, 2, 3, 4, 5, 6, 7]
array3 = array.shift(7) # array3 is now [8, 9, 10, 11, 12, 13, 14]

Note that the shift method edits your original array as well.

By the way, this is pure Ruby (the programming language), no Rails (the framework) here! Hope this helps.

Yurii Stefaniuk · Answer 2 · 2022-06-13T11:59:27.880

I think you need each_slice here:

res = array.each_slice(7).to_a

And you will get array with subarrays length 7 each. Last element will have remaining:

# outputs below
[
   [1, 2, 3, 4, 5, 6, 7],
   [8, 9, 10, 11, 12, 13, 14],
   [15, 16, 17, 18, 19, 20, 21],
   [22, 23, 24, 25, 26, 27, 28],
   [29, 30, 31, 32, 33, 34, 35],
   [36, 37, 38, 39, 40]
]

And then you can use each to go through elements

res.each { |subarray| # do with subarray what you need }

Or you can get any element you want by using these methods:

first_subarray = res.first
second_subarray = res.second
last_subarray = res.last

# or by index

third_subarray = res[2]

And key thing here that your initial array won't be reflected

Cary Swoveland · Accepted Answer · 2022-06-13T19:43:54.733

Here are three ways to do that.

Use Array#slice!

array = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
         16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
         29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]

array2 = array.slice!(0,7)
  #=> [1, 2, 3, 4, 5, 6, 7]
array3 = array.slice!(0,7)
  #=> [8, 9, 10, 11, 12, 13, 14]

Now,

array
  #=> [15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
  #    28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]

If array is not to be mutated use Array#slice and add an additional variable (say, array1).

array2 = array.slice(0..6)
  #=> [1, 2, 3, 4, 5, 6, 7]
array3 = array.slice(7..13)
  #=> [8, 9, 10, 11, 12, 13, 14]
array1 = array.slice(14..)
  #=> [15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
  #    28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]

Use Enumerable#slice_before

i = 0
array2, array3, array = array.slice_before { [8, 15].include?(i += 1) }.to_a
  #=> [[1, 2, 3, 4, 5, 6, 7],
  #    [8, 9, 10, 11, 12, 13, 14],
  #    [15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
  #     28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]]

Now,

array2
  #=> [1, 2, 3, 4, 5, 6, 7]
array3
  #=> [8, 9, 10, 11, 12, 13, 14]
array
  #=> [15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
  #    28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]

If array is not to be mutated replace array with array1 on the left side of the equals sign.

Partition indices and use Array#values_at

array2, array3, array = [[*0..6], [*7..13], [*14..(array.size-1)]].
  map { |a| array.values_at(*a) }
  #=> [[1, 2, 3, 4, 5, 6, 7],
  #    [8, 9, 10, 11, 12, 13, 14],
  #    [15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
  #     28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40]]

If array is not to be mutated replace array with array1 on the left side of the equals sign.

How to enter data into a new array

3 Answers3