Adding values of multi dimensional array

Question

I'm working with chart data. I have three sets of data from three sources, and I'm trying to add them together by their year into a new away. In my example, the years are 0, 1, 2.

visual:

data = [[[year, value], [year, value], [year, value]],
       [[year, value], [year, value], [year, value]],
       [[year, value], [year, value], [year, value]]]

Here is an example with actual data:

data = [[[0, 1], [1, 2], [2, 3]],
       [[0, 4], [1, 5], [2, 6]],
       [[0, 7], [1, 8], [2, 9]]]

I'm trying to get the following result:

data = [[0, 12], [1, 15], [2, 18]]

To add to complexity, it won't always be three sets of data, it may be one set or twelve sets, any number.

Any help is greatly appreciated.

show us the code you have tried

Gavriel
– Gavriel

2016-01-30 19:01:45 +00:00
Commented Jan 30, 2016 at 19:01 — Gavriel
– Gavriel, Commented Jan 30, 2016 at 19:01

Wand Maker · Accepted Answer · 2016-01-31 07:03:34Z

Solution:

data.map(&:to_h).reduce({}) {|memo, h| memo.merge(h) {|_,v1,v2| v1 + v2} }.to_a

Explanation:

Step 1: Convert the data array into array of hashes

data_hash = data.map(&:to_h)
#=> [{0=>1, 1=>2, 2=>3}, {0=>4, 1=>5, 2=>6}, {0=>7, 1=>8, 2=>9}]

Step 2: Reduce the array of hash by merging each hash with one another, while ensuring that values are added together for a given key.

reduced_hash = data_hash.reduce({}) {|memo, h| memo.merge(h) {|_,v1,v2| v1 + v2} }  
#=> {0=>12, 1=>15, 2=>18}

We use empty hash {} as initial value of memo, and merge each hash present in data_hash array with it - the block to merge will ensure that when a key is being merged, its values are added up so that eventually we end up with sum of all values of that key

Step 3: Use to_a on the hash to get array result

 reduced_hash.to_a
 #=> [[0, 12], [1, 15], [2, 18]]

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