Menu
I have a hash:
hash = {"a_1_a" => "1", "a_1_b" => "2", "a_1_c" => "3", "a_2_a" => "3",
"a_2_b" => "4", "a_2_c" => "4"}
What's the best way to get the following sub-hashes:
[{"a_1_a" => "1", "a_1_b" => "2", "a_1_c" => "3"},
{"a_2_a" => "3", "a_2_b" => "4", "a_2_c" => "4"}]
I want them grouped by the key, based on the regexp /^a_(\d+)/. I'll have 50+ key/value pairs in the original hash, so something dynamic would work best, if anyone has any suggestions.
396
You can only store scalar values in a hash. References, however, are scalars. This solves the problem of storing multiple values for one key by making $hash{$key} a reference to an array containing values for $key .
Accessing a specific element in a nested hash is very similar to a nested array. It is as simple as calling hash[:x][:y] , where :x is the key of the hash and :y is the key of the nested hash.
To add another hash to an array, we first initialize the array with our data. Then, we use push to push the new hash to the array. The new hash should have all of its data. As shown below, you can see the difference between the two arrays before and after pushing a new hash.
From perldoc perldata: If you evaluate a hash in scalar context, it returns false if the hash is empty. If there are any key/value pairs, it returns true; more precisely, the value returned is a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash.
If you're only concerned about the middle component you can use group_by to get you most of the way there:
hash.group_by do |k,v|
k.split('_')[1]
end.values.map do |list|
Hash[list]
end
# => [{"a_1_a"=>"1", "a_1_b"=>"2", "a_1_c"=>"3"}, {"a_2_a"=>"3", "a_2_b"=>"4", "a_2_c"=>"4"}]
The final step is extracting the grouped lists and combining those back into the required hashes.
82
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
