How to calculate the sum of array inside hash ruby

Question

Hai i am creating a json file with my data and i need to calculate the hours before i save it into the database

I am assigning that hash into a variable payload and tried doing this but it returns me an error TypeError (no implicit conversion of Symbol into Integer):

total_hours = @payload.sum{|activity| activity[:hours].to_f}

Hash before converting to json

{:activities=>
  [{:project=>1,
    :activity=>"my activity",
    :hours=>0.2e1,
    :date=>Sat, 10 Aug 2019 00:00:00 UTC +00:00},
   {:project=>2,
    :activity=>"Tester",
    :hours=>0.2e1,
    :date=>Thu, 01 Aug 2019 00:00:00 UTC +00:00},
   {:project=>2,
    :activity=>"Tester",
    :hours=>0.3e1,
    :date=>Thu, 01 Aug 2019 00:00:00 UTC +00:00}]}

I need to sum the hours of my array which is inside the hash. Thanks

Try total_hours = @payload[:activities].sum{|activity| activity[:hours].to_f} — jvillian
– jvillian, Commented Aug 14, 2019 at 5:00
@jvillian Thank you so much it worked!! Can you say what was i doing wrong — Amal T S
– Amal T S, Commented Aug 14, 2019 at 5:04
You have targeted object instead of array. thats the reason [:activities] is array of obj. — 7urkm3n
– 7urkm3n, Commented Aug 14, 2019 at 5:09
Oh my bad, Thank you. Can you add this as an answer so i can choose it as my answer so it would be helpful to others too. — Amal T S
– Amal T S, Commented Aug 14, 2019 at 5:12

Sebastián Palma · Accepted Answer · 2019-08-18 14:42:26Z

2

If you are using Rails, here is a short way:

@payload[:activities].pluck(:hours).reduce(:+)

edited Aug 18, 2019 at 14:42

Sebastián Palma

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answered Aug 14, 2019 at 13:12

Gustavo Toro

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2 Comments

Sebastián Palma Over a year ago

@payload[:activities].sum(:hours) will work and is shorter.

Gustavo Toro Over a year ago

No, you'll have an undefined method + for :hours Symbol. Check it.

jvillian · Accepted Answer · 2019-08-14 05:11:11Z

You should use:

total_hours = @payload[:activities].sum{|activity| activity[:hours].to_f}

You see, what you're wanting to do is, essentially:

[
  {
    :project=>1,
    :activity=>"my activity",
    :hours=>0.2e1,
    :date=>Sat, 10 Aug 2019 00:00:00 UTC +00:00
  },
  {
    :project=>2,
    :activity=>"Tester",
    :hours=>0.2e1,
    :date=>Thu, 01 Aug 2019 00:00:00 UTC +00:00
  },
  {
    :project=>2,
    :activity=>"Tester",
    :hours=>0.3e1,
    :date=>Thu, 01 Aug 2019 00:00:00 UTC +00:00
  }
].sum{|activity| activity[:hours].to_f}

But, you're calling .sum on the @payload variable, which is a hash. What you want is the value of the hash that is associated with the key :activities. Thus, you need to call .sum on @payload[:activities] where @payload[:activities] returns the array above.

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