Rails merge array into array of arrays

Question

I'm new to Ruby on Rails and I have a weird array situation that I'm unable to figure out how to execute efficiently.

I have this starting array of arrays:

[["6884", true], ["8456", false], ["5631", false]]

Then I have another 1D array:

["6884", "8023", "9837"]

I want to merge the 1D array into the array of arrays by appending the value to the end of the array at the same index in the 2D array.

So the final product should be:

[["6884", true, "6884"], ["8456", false, "8023"], ["5631", false, "9837]]

So the value at index 0 in the 1D array is appended to the end of the array at index 0 in the 2D array, and so on for each element in the 1D array. Is there an easy Ruby way to accomplish this?

Mehmet Adil İstikbal · Accepted Answer · 2022-08-22 18:12:08Z

6

You can do it with zip and flatten methods like this:

a = [["6884", true], ["8456", false], ["5631", false]]
b = ["6884", "8023", "9837"]

a.zip(b)
# [[["6884", true], "6884"], [["8456", false], "8023"], [["5631", false], "9837"]]

# Then use flatten to this array:
a.zip(b).map(&:flatten)
# [["6884", true, "6884"], ["8456", false, "8023"], ["5631", false, "9837"]]

answered Aug 22, 2022 at 18:12

Mehmet Adil İstikbal

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1 Comment

engineersmnky Over a year ago

Only note is that this could be consumptive on a larger data set as it creates N * N + 2 new Arrays where N = a.size

Tom Lord · Accepted Answer · 2022-08-22 18:16:38Z

5

Further to Mehmet Adil İstikbal's answer, here's another approach -- just to show that There's More Than One Way To Do It:

a = [["6884", true], ["8456", false], ["5631", false]]
b = ["6884", "8023", "9837"]

a.map.with_index { |item, index| item.push(b[index]) }
# => [["6884", true, "6884"], ["8456", false, "8023"], ["5631", false, "9837"]]

answered Aug 22, 2022 at 18:16

Tom Lord

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2 Comments

Acheese Over a year ago

This also works well, I just prefer the cleanliness of Mehmet's answer. Thank you!

Cary Swoveland Over a year ago

It should be noted that this mutates a.

Cary Swoveland · Accepted Answer · 2022-08-22 23:20:32Z

3

a2 = [["6884", true], ["8456", false], ["5631", false]]
a1 = ["6884", "8023", "9837"]

a2.zip(a1).map { |e2, e1| [*e2, e1] }

or, to avoid the creation of the temporary array a2.zip(a1),

a1.each_index.map { |i| [*a2[i], a1[i]] }

Both return

[["6884", true, "6884"], ["8456", false, "8023"], ["5631", false, "9837"]]

Note that neither expression mutates a2 or a1. See Array#each_index (which, without a block, returns an enumerator) and Enumerable#map.

edited Aug 22, 2022 at 23:20

answered Aug 22, 2022 at 18:21

Cary Swoveland

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1 Comment

engineersmnky Over a year ago

I understood where you were going. Iterative methods, especially ones that take a block, can be confusing in ruby because some return immediately and others return Enumerators. zip's block is extra confusing since it yields the zipped elements but always returns nil.

Stefan · Accepted Answer · 2022-08-22 18:31:56Z

2

If you want to modify the first array you can pass a block to zip to append the latter elements to the corresponding sub-array:

a = [["6884", true], ["8456", false], ["5631", false]]
b = ["6884", "8023", "9837"]

a.zip(b) { |ary, el| ary << el }

a
# => [["6884", true, "6884"], ["8456", false, "8023"], ["5631", false, "9837"]]

answered Aug 22, 2022 at 18:31

Stefan

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