CODEWITHSUNDEEP
javascriptarrays
Jason Nichols
Jason Nichols

Reputation: 3760

Returning an Array in JavaScript

I was inspired by this question to write a recursive function in JavaScript to add elements of an array and return an array accordingly.

in Pseudocode

arr = [1,2,3,4,5,6]
func (arr,2) = > [1+3+5, 2+4+6]
                 [9,12]
func (arr,3) = > [1+4,2+5,3+6]
                 [5,7,9]

So I wrote a fiddle, here.

var input = [1,2,3,4,5,6,7,8,9];

function tupleAdd(tuple,i,p,t,output){
    if(typeof t == "undefined")
        t=0;
    if(typeof p == "undefined")
        p=0;
    if(typeof output == "undefined")
        output = [];
    if(typeof output[t] =="undefined")
        output[t]=0;

    output[t]+=i[p];
    p++;
    t++;
    t>=tuple?t=0:null;
    if(p<i.length)
        tupleAdd(tuple,i,p,t,output);
    else{
        console.log(output);
        return(output);
    }
}

x = tupleAdd(3,input);
console.log(x);

My function works, as the first console.log() shows the appropriate values. What weirds me out is that when I return output (with or without parens), and try and log it again, I get undefined.

I find this deeply unsettling. Can anyone shed some light on why the return value is different than the console.log value?

Upvotes: 3

Views: 424

Answers (3)

Igor Benikov
Igor Benikov

Reputation: 897

function doTuple(arr, tuple){

    if(!arr.length){
        return tuple;
    }

    var el = arr.splice(0,1);

    el % 2 ? tuple.evens += +el : tuple.ods += +el;

    return doTuple(arr, tuple);
}

console.log(doTuple([1,2,3,4,5], {evens:0,ods:0}));

Upvotes: -2

BenM
BenM

Reputation: 53198

You need to return the value of the recursive call:

var input = [1,2,3,4,5,6,7,8,9];

function tupleAdd(tuple,i,p,t,output){
    if(typeof t == "undefined")
        t=0;
    if(typeof p == "undefined")
        p=0;
    if(typeof output == "undefined")
        output = [];
    if(typeof output[t] =="undefined")
        output[t]=0;

    output[t]+=i[p];
    p++;
    t++;
    t>=tuple?t=0:null;
    if(p<i.length)
        return tupleAdd(tuple,i,p,t,output);
    else{
        console.log(output);
        return(output);
    }
}

x = tupleAdd(3,input);
console.log(x);

Upvotes: 2

epascarello
epascarello

Reputation: 207501

Your recursion is broken. You are getting undefined since you do not have a return on the function call inside. 

tupleAdd(tuple,i,p,t,output);

needs to be

return tupleAdd(tuple,i,p,t,output);

Upvotes: 3

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