How to set nested hash in ruby dynamically?

Question

Lets say I have a nested hash:

h = { 'one' =>
        {'two' =>
            {'three' => 'a'}
        }
     }

I can change it like this:

h['one']['two']['three'] = 'b'

How can I change the nested value with a variable as a key?

Let's say I have the following variable:

key = "one.two.three"

To access it dynamically, I use the following:

key.split('.').inject(h,:[])

But of course setting it like this does not work:

key.split('.').inject(h,:[]) = 'b' # fails

So how can I set the value of a nested hash dynamically?

sawa · Accepted Answer · 2013-01-12 15:28:10Z

20

Hash#[]= is a single method. You cannot do Hash#[] all the way to the last key and do = to it. Rather, leave out the last key and do Hash#[]= individually on it.

*key, last = key.split(".")
key.inject(h, :fetch)[last] = "b"

answered Jan 12, 2013 at 15:28

sawa

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Damian C. Rossney · Accepted Answer · 2023-08-15 23:23:20Z

0

Building on sawa's answer, in modern Ruby with Hash#dig, this becomes even simpler:

    
*key, last = key.split(".")
    
h.dig(key)[last] = "b"

answered Aug 15, 2023 at 23:23

Damian C. Rossney

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