CODEWITHSUNDEEP
arraysruby-on-railsjson
rjsnavarette
rjsnavarette

Reputation: 13

How to group json array and sum its total per week?

I have an array

    [
        {
            "week_year": "49-2021",
            "total": 6.5
        },
        {
            "week_year": "45-2021",
            "total": 28.5
        },
        {
            "week_year": "45-2021",
            "total": 6.5
        },
        {
            "week_year": "44-2021",
            "total": 6.5
        },
        {
            "week_year": "46-2021",
            "total": 14.5
        }
    ]

I want to group it by the same week_year and sum its total per week. Any other way to do that?

Upvotes: 0

Views: 334

Answers (3)

Cary Swoveland
Cary Swoveland

Reputation: 110685

If arr is the array given in the question one could write

arr.each_with_object(Hash.new(0)) { |g,h| h[g[:week_year]] += g[:total] }
  #=> {"49-2021"=>6.5, "45-2021"=>35.0, "44-2021"=>6.5, "46-2021"=>14.5}

This makes a single pass through the array and requires less memory than does the use of Enumerable#group_by. Arguably, it also reads better. Whether it's faster is an open question.

This employs the form of Hash::new that takes an argument--called the default value--and no block. If a hash h is so-defined, then, possibly after keys have been added, if h does not have a key k, h[k] returns the default value. The default value is commonly chosen to be zero, as it is here.

The expression

h[g[:week_year]] += g[:total]

expands to

h[g[:week_year]] = h[g[:week_year]] + g[:total]

so if h does not have a key g[:week_year] this becomes

h[g[:week_year]] = 0 + g[:total]

Upvotes: 1

Sebastián Palma
Sebastián Palma

Reputation: 33420

If the output needed is like { week_year => total } then you can use a combination of group_by, transform_values and sum:

arr
  .group_by { |hash| hash[:week_year] }
  .transform_values { |arr| arr.sum { |hash| hash[:total] } }
# {"49-2021"=>6.5, "45-2021"=>35.0, "44-2021"=>6.5, "46-2021"=>14.5}

Upvotes: 1

razvans
razvans

Reputation: 3251

You can use group_by in combination with transform_values:

array.group_by { |a| a[:week_year] }
     .transform_values { |values| values.sum { |value| value[:total] } }

Which will return:

{
 "49-2021" => 6.5,
 "45-2021" => 35.0,
 "44-2021" => 6.5,
 "46-2021" => 14.5
}

Upvotes: 0

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