Split an array in ruby based on some condition

Question

I have an array named @level1 which has a value like this:

[
  [3.1, 4],
  [3.0, 7],
  [2.1, 5],
  [2.0, 6],
  [1.9, 3]
]

I want to split this into two arrays such that the first array (@arr1) contains the values till 2.1 and the second array (@arr2) contains values after it.

After doing that, I would reverse-sort my second array by doing something like this:

@arr2 = @arr2.sort_by { |x, _| x }.reverse

I would then like to merge this array to @arr1. Can someone help me how to split the array and then merge them together?

@arr1 = { [3.1, 4], [3.0, 7]} @arr2 = { [2.1, 5], [2.0, 6], [1.9, 3]} Then I will reverse sort @arr2 which will give me the follwoing: @arr2 = { [1.9, 3] , [2.0, 6], [2.1, 5]} And then i would merge these 2 arrays — Pi Horse
– Pi Horse, Commented Oct 25, 2012 at 19:38
possible duplicate of Best way to split arrays into multiple small arrays in ruby — akostadinov
– akostadinov, Commented Jul 2, 2015 at 12:13

Nikita Fedyashev · Accepted Answer · 2021-07-01 10:15:06Z

100

Try the partition method

@arr1, @arr2 = @level1.partition { |x| x[0] > 2.1 }

The condition there may need to be adjusted, since that wasn't very well specified in the question, but that should provide a good starting point.

edited Jul 1, 2021 at 10:15

Nikita Fedyashev

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answered Oct 25, 2012 at 19:46

qqx

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3 Comments

SwiftMango Over a year ago

You probably want to use x[0] <= 2.1

qqx Over a year ago

@texasbruce No, arr1 is supposed to contain the larger values, so the condition should not be reversed. In any case, since the question didn't do a very good job of specifying the exact condition I'm not too concerned about getting that exactly correct here.

Pi Horse Over a year ago

Guys it says : undefined method `>' for ["3.1"]:Array

Nikita Fedyashev · Accepted Answer · 2021-07-01 10:16:22Z

0

something like this?

arr = [
  ["3.1", 4],
  ["3.0", 7],
  ["2.1", 5],
  ["2.0", 6],
  ["1.9", 3]
]

arr1, arr2 = arr.inject([[], []]) do |f,a|
  a.first.to_f <= 2.1 ? f.last << a : f.first << a; f
end

arr = arr1 + arr2.reverse
# => [["3.1", 4], ["3.0", 7], ["1.9", 3], ["2.0", 6], ["2.1", 5]]

edited Jul 1, 2021 at 10:16

Nikita Fedyashev

19.3k15 gold badges58 silver badges110 bronze badges

answered Oct 25, 2012 at 19:43

user904990

4 Comments

Pi Horse Over a year ago

It says undefined method `<=' for ["3.0"]:Array

user904990 Over a year ago

the code in my answer works well on 1.8.7(as on all other versions), here is the proof

Pi Horse Over a year ago

I think the first element that is 3.1, 3.0, 2.1 and so on, in each row is considered as a string. How do I convert that to an integer. It is not able to compare because it a a string.

Pi Horse Over a year ago

ok i managed to convert that to float and it works now. Thanks

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