CODEWITHSUNDEEP
arraysrubysum
Bruno Morales
Bruno Morales

Reputation: 203

Error summing an array

So I'm new to ruby, I was practicing doing hackerrank excercices and when I had to sum an array I got the following error:

solution.rb:6:in +': nil can't be coerced into Integer (TypeError) from solution.rb:6:inblock in simpleArraySum' from solution.rb:5:in each' from solution.rb:5:insimpleArraySum' from solution.rb:15:in `'

Code:

def sum(n, arr)
    sum = 0
    for i in (0..n) do
        sum += arr[i]
    end
    return sum
end

Similar js code:

const sum = function (n, arr) {
    let sum = 0;
        for (let i = 0; i < n; i++) {
            sum += arr[i];
    }
    return sum;
};

Upvotes: 0

Views: 522

Answers (3)

J. Gary
J. Gary

Reputation: 9

As others have noted, the best practice here is probably to just use the arr#each enumerable method (q.v.)

That aside: I'm not sure what your variable n is supposed to be, but I'm guessing it's the number of elements in your array. I'd offer that it's better practice to use the arr#length method (which returns the number of elements in the array; subtracting 1 syncs the loop with a zero-indexed array.)

test_arr = [1,2,3,4,5]

def sum(arr)
    sum = 0
    for i in (0..arr.length-1) do
        sum += arr[i]
    end
    return sum
end

sum(test_arr) => 15

(FYI: Using arr.length is probably better practice in JavaScript as well (although using the JS .forEach or .reduce callback functions might be even better.))

for (let i = 0; i < arr.length -1; i++) {

Upvotes: 0

peter
peter

Reputation: 42192

Your n is bigger than the number of elements in your array-1 so it tries to sum a nil.

Here a better way to do this in Ruby, with an each in stead of a for which is seldom used. If you want to use a for, you could get the length of the array from arr.length instead of the parameter n.

def sum arr
  sum = 0
  arr.each do |e|
    sum += e
  end
  sum
end

The real Ruby way would be the following. You inject a variable filled with 0 and enumerate each element of the array. The variables between the || are this variable, used to remember our sum and the element that is being enumerated.

[1,5].inject(0){|sum, e| sum + e } 
=>6

or shorter

[1,5].inject(0, &:+) 
=>6

or still better/shorter/readable (thus Ruby like) if you use Ruby 2.4

[1, 5].sum
=> 6

Upvotes: 4

jk_
jk_

Reputation: 755

The error is telling you that the addition operation is unsuccessful because one or more of the values is nil.

In this case, are you sure that when i==n there will be a value at i[n]?

Remember, arrays are 0-indexed. Meaning, if the length of the array is n, the index of the nth value will actually be n-1.

So when your loop hits n, you end up trying to evaluate sum += nil, which produces the error you are seeing.

Upvotes: 1

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