I have a 2D array with each row like:
['John', 'M', '34']
I want to map into an array of Hash with each hash like:
{:Name=>"John", :Gender=>"M", :Age=>"34"}
Is there an elegant way of doing that?
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5 Answers
array_of_rows.map { |n,g,a| { Name: n, Gender: g, Age: a } }
or
array_of_rows.map { |row| %i{Name Gender Age}.zip(row).to_h }
They produce the same result, so pick the one you find clearer. For example, given this input:
array_of_rows = [
['John', 'M', '34'],
['Mark', 'M', '49']
]
either expression will yield this output:
[{:Name=>"John", :Gender=>"M", :Age=>"34"},
{:Name=>"Mark", :Gender=>"M", :Age=>"49"}]
2 Comments
Cary Swoveland
When I see problems like this I generally ask myself, "What if the data changes in future, the number of keys, for example?". Best to avoid having to change the code, of course, so I prefer #2, but would not hardwire
%i{Name Gender Age}.
Mark Reed
Sure. Ideally you'd have some metadata associated with the array you could use instead of hard-coding the key names; perhaps it was read from a CSV file, and the first row contains headers that can be repurposed.
You could try using zip and then to_h (which stands for to hash)
For example:
[:Name, :Gender, :Age].zip(['John', 'M', '34']).to_h
=> {:Name=>"John", :Gender=>"M", :Age=>"34"}
Comments
people = [['John', 'M', '34']]
keys = %i{Name Gender Age}
hashes = people.map { |person| keys.zip(person).to_h }
# => [{:Name=>"John", :Gender=>"M", :Age=>"34"}]
Basically the way I turn combine two arrays into a hash (one with keys, one with values) is to use Array#zip. This can turn [1,2,3] and [4,5,6] into [[1,4], [2,5], [3,6]]
This structure can be easily turned into a hash via to_h
Comments
array_of_rows = [
['John', 'M', '34'],
['Mark', 'M', '49']
]
keys = ['Name', 'Gender', 'Age']
[keys].product(array_of_rows).map { |k,v| k.zip(v).to_h }
#=> [{"Name"=>"John", "Gender"=>"M", "Age"=>"34"},
# {"Name"=>"Mark", "Gender"=>"M", "Age"=>"49"}]
or
keys_cycle = keys.cycle
array_of_rows.map do |values|
values.each_with_object({}) { |value, h| h[keys_cycle.next]=value }
do
Comments
Here is one more way to do this
array_of_rows = [
['John', 'M', '34'],
['Mark', 'M', '49']
]
keys = [:Name, :Gender, :Age]
array_of_rows.collect { |a| Hash[ [keys, a].transpose] }
#=>[{:Name=>"John", :Gender=>"M", :Age=>"34"}, {:Name=>"Mark", :Gender=>"M", :Age=>"49"}]
