How do I check to see if an array of arrays has a value within the inner arrays?

Question

Say I have an array of arrays that looks like this:

[[1830, 1], [1859, 1]]

What I want to do is quickly scan the internal arrays to see if any of them contain the number 1830. If it does, I want it to return the entire array that includes the number 1830, aka [1830, 1] from the above example.

I know for a normal array of values, I would just do array.include? 1830, but that doesn't work here, as can be seen here:

@add_lines_num_start
#=> [[1830, 1], [1859, 1]]
@add_lines_num_start.include? 1830
#=> false
@add_lines_num_start.first.include? 1830
#=> true

How do I do that?

Suppose the array was [[1830,1], [2, 1830], [3, 1492]] and the number of interest was 1830. Is [[1830,1], [2, 1830]] to be returned? — Cary Swoveland
– Cary Swoveland, Commented Mar 3, 2017 at 8:18

Community · Accepted Answer · 2020-06-20 09:12:55Z

6

a = [[1830, 1], [1859, 1]]
a.find { |ar| ar.grep(1830) }
#=> [1830, 1]

References:

edit 1

As @Ilya mentioned in comment, instead of traversing the whole array with grep you could use the method to return the boolean once element that matches the condition is found:

a.find { |ar| ar.include?(1830) }

References:

Enumerable#include?

edit 2 (shamelessly stolen from @Cary's comment under OP)

In case you'll have more than one matching array in your array, you can use Enumerable#find_all:

a = [[1830, 1], [1859, 1], [1893, 1830]]
a.find_all { |ar| ar.include?(1830) }
#=> [[1830, 1], [1893, 1830]]

edited Jun 20, 2020 at 9:12

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answered Mar 3, 2017 at 7:52

Andrey Deineko

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4 Comments

marcamillion Over a year ago

Perfect. This is exactly what I am looking for. Thanks!

Andrey Deineko Over a year ago

@marcamillion no probs :)

Ilya Over a year ago

include? seems to be more readable, moreover: it's more efficient, you don't scan a whole array in this case.

Andrey Deineko Over a year ago

@AlexGolubenko yea, select is an alias of find_all :)

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