CODEWITHSUNDEEP
ruby
witkacy26
witkacy26

Reputation: 101

Ruby: NoMethodError: undefined method `+' for nil:NilClass

Would anybody have an idea, why following code returns error:

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
add = {"M9788375085969"=>1, "M9788392289760"=>2, "NEW9788392289753"=>1 }

add.each do |key, value|
  stock[key] += value
end

NoMethodError: undefined method `+' for nil:NilClass

while similar thing works fine:

key = "M9788375085969"
value = 1
stock[key] += value
=> 6

Upvotes: 0

Views: 758

Answers (4)

Arup Rakshit
Arup Rakshit

Reputation: 118289

The key "NEW9788392289753" is not present in the Hash stock,but present in add hash. See below :

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
stock['NEW9788392289753'] # => nil
nil.respond_to?(:+) # => false # means NilClass don't has method called :+

Thus nil.+(value) throwing a valid error. Do as below :

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
add = {"M9788375085969"=>1, "M9788392289760"=>2, "NEW9788392289753"=>1 }

add.each do |key, value|
  p stock[key] += value if stock.has_key?(key) # it will take care of the error.
end

output

6
7

As per OP's comment I would do as :

add.each do |key, value|
  if stock.has_key?(key) 
     stock[key] += value 
  else
     stock[key] = value
  end
end

Upvotes: 2

steenslag
steenslag

Reputation: 80085

Another way of treating non-existent keys is providing a default of zero:

stock = {"M9788375085969"=>5, "M9788392289760"=>5, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2}
add = {"M9788375085969"=>1, "M9788392289760"=>2, "NEW9788392289753"=>1 }

stock.default = 0 

add.each do |key, value|
  stock[key] += value
end

p stock #=> {"M9788375085969"=>6, "M9788392289760"=>7, "M9788389371461"=>1, "M9788389371447"=>3, "M9788392289761"=>2, "NEW9788392289753"=>1}

Upvotes: 1

glasz
glasz

Reputation: 2565

because the key NEW9788392289753 from add is not contained in stock.

Upvotes: 2

kostja
kostja

Reputation: 61578

There is one key in your add hash that is missing in your stock hash : "NEW9788392289753".

When executing stock["NEW9788392289753"], nil is returned, as the key is not mapped.

Upvotes: 3

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