How to access an array element inside a hash in Ruby

Question

I have a hash of arrays of coordinates of locations like this:

cities = {
  "l10"=> [41.84828634806966,-87.61184692382812],
  "l11"=> [41.86772008597142,-87.63931274414062],
  "l12"=> [41.88510316124205,-87.60498046875],
  "l13"=>[41.84930932360913,-87.62420654296875]
}

To access the second value in the first array, I tried:

puts cities[0][1][1]

I want it to print out -87.61184692382812, but it doesn't. It gives me an error.

I am trying to iterate over the hash. Accessing it by using

puts cities["l10"][1]

doesn't work. But

puts cities[0][1][1]

worked when I converted it into an array.

@rotgers that's not going to work because cities is not an array. "first" doesn't make a whole lot of sense for a hash. — jordanm, Apr 21 '17 at 22:39
Can u make it clear please. what you trying to achieve by this ?? — Vishal Taj PM, Apr 22 '17 at 07:18

score 4 · Answer 1 · answered Apr 21 '17 at 22:39

You can do that if you make your hash an array, otherwise for the first access you have to use a key (well, ok, even 0 can be a key but is not present in your hash)

cities.to_a[0][1][1]
 => -87.61184692382812 

cities["l10"][1]
 => -87.61184692382812

score 1 · Accepted Answer · edited Apr 21 '17 at 23:44

1

Here's one way to access the second value of the first key of your hash:

cities.values.first[1]
# => -87.61184692382812

This fetches the value of your first key (in this case it's that first array in the hash), and then retrieves by index the second element of that array.

edited Apr 21 '17 at 23:44

the Tin Man

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answered Apr 21 '17 at 22:39

Zoran

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score 0 · Answer 3 · answered Apr 21 '17 at 23:16

Use Hash#dig on Hashes

A Hash isn't indexable, because it's not guaranteed to be ordered (although pragmatically, recent MRI implementations maintain insert order). Instead, you need to look up by key and then index into the Array stored there as a value. In recent versions with support for Hash#dig, you can use the following syntax:

cities.dig 'l10', 1
#=> -87.61184692382812

Alternatively, you can convert the Hash object into an Array of arrays, and then index as you are trying to do in the original post. For example:

cities.to_a[0][1][1]
#=> -87.61184692382812

How to access an array element inside a hash in Ruby

3 Answers3

Use Hash#dig on Hashes