Ruby dynamically adding keys and values to hashes

Question

Hello I need a bit of help.

Here is what I want to do.

Check if hash already has key based on a variable
If key already exists add new value to key
If key does not exists create new key and add new value to it

Here is what I got and it has many issues:

if @agencyList.has_key?(domain)
    @agencyList[domain] << match
else
    @agencyList[domain] = match
end

Thanks!

Also, consider using the multimap gem. Then (assuming you use a Multimap instance for @agencyList) you'd use @agencyList[domain] = match to add an entry, in all cases. — C. K. Young
– C. K. Young, Commented Mar 21, 2014 at 3:13
There's a pretty strong convention in Ruby of only using snake_case for variable names. CamelCase is detected by the parser and is reserved for constants (class names and module names). Using camelCase with a lowercase beginning will confuse basically everybody. — Alex Altair
– Alex Altair, Commented Mar 21, 2014 at 3:16

Windor C · Accepted Answer · 2014-03-21 03:33:17Z

4

Suppose your hash has values of Array type, and add new value to the array rather than replacing it. The follows can work:

@agency_list[domain] ||= []
@agency_list[domain] << match

Enjoy!

answered Mar 21, 2014 at 3:33

Windor C

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2 Comments

Cary Swoveland Over a year ago

...which you'll often see written (@agency_list[domain] ||= []) << match.

Windor C Over a year ago

@CarySwoveland yeah.., it goes further.

Alex Altair · Accepted Answer · 2014-03-21 03:18:26Z

1

Are the values of the keys arrays that you want to add the new value to, or just objects that you want to overwrite?

If they're arrays you want to add to, this should work;

if @agency_list.has_key?(domain)
  @agency_list[domain] << match
else
  # This way you can create the array and put the value in at the same time
  @agency_list[domain] = [match]
end

If they're just objects you want to overwrite, you don't even have to check if they key is there;

@agency_list[domain] = match

edited Mar 21, 2014 at 3:18

answered Mar 21, 2014 at 3:13

Alex Altair

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1 Comment

user1358886 Over a year ago

I don't want to overwrite. The problem is the value I add are all bunched into one element. I need them to be in separate elements.

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