CODEWITHSUNDEEP
ruby
user3467349
user3467349

Reputation: 3191

Sum of an array

So in Python sum([]) will yield 0, which is pretty important.

Whereas in ruby [].reduce(:+) will give nil, of course the ternary operator isn't a replacement, because: 

(my_complicated_mapping).empty? ? 0 : (my_complicated_mapping).reduce(:+)

Will call my_complicated_mapping twice. Therefore the obvious method is: 

res = my_complicated_mapping
res = (res.empty? ? 0 : res.reduce(:+))

I think there must be a neater way to do this though.

Upvotes: 1

Views: 96

Answers (4)

mikej
mikej

Reputation: 66263

With reduce you can specify the initial value as the first parameter e.g.

my_complicated_mapping.reduce(0, :+)

then if the list is empty you'll get 0 instead of nil. You can check the different alternative ways of using reduce here.

or if using a block for reduce it would be: 

my_complicated_mapping.reduce(0) { |sum, n| sum + n }

i.e. a single parameter with with initial value and supplying your block.

It's important to understand why reduce returns nil in the case of the empty array: If you don't specify an explicit initial value for memo, then the first element of the array is used as the initial value of memo, which of course doesn't exist in the empty case.

Upvotes: 4

pangpang
pangpang

Reputation: 8821

You also can use inject:

my_complicated_mapping.inject(0) { |sum, e| sum + e }

Upvotes: 0

shivam
shivam

Reputation: 16506

You can use to_i to convert nil to 0

[].reduce(:+).to_i
# => 0

Incase Array contains float values, using to_f can help:

[].reduce(:+).to_f
# => 0.0

Upvotes: 2

claasz
claasz

Reputation: 2134

Why not give 0 as initial parameter? Like

my_complicated_mapping.reduce(0, :+)

Upvotes: 1

Related Questions