Question about creating 2d arrays

[u/[deleted]]

function pair(str) {
    var string = str.split("");
    var newArr = [];
    for (var i = 0; i < string.length; i++) {
        var temp = [];
        if (str[i] === "G") {
            temp.push(str[i] + "C");
        } else if (str[i] === "C") {
            temp.push(str[i] + "G");
        } else if (str[i] === "A") {
            temp.push(str[i] + "T");
            } else if (str[i] === "T") {
            temp.push(str[i] + "A");
        }
        newArr.push(temp);
        }
        return newArr;
    }

pair("GCG");

Im getting [ [ 'GC' ], [ 'CG' ], [ 'GC' ] ] If I didn't create the empty temp array where I pushed in the letters BEFORE pushing the temp array into the newArr outside of the loop, I would get only one array -- [ 'GC' , 'CG', 'GC' ]. Can someone please explain why I am getting a 2d array now? Like I thought it just pushing every letter (plus the second letter) into the temp array and THEN pushes it all to the newArr- but that can't be it because then I would again not get a 2d array-meaning that for example: it pushes first the G+C into temp, then RIGHT AWAY into newer, then again pushes A+T into temp and then right away into newer etc and I don't understand why it pushes it right away into newArr without finishing first the loop? Thanks

[u/Volv]

You are pushing strings into a temp array and then pushing a temp array onto the result array.
Commented to show the workings.
 

function pair(str) {
  var string = str.split("");
  var newArr = [];                // Result Array []
  for (var i = 0; i < string.length; i++) {
    var temp = [];                // Make temp Array []
    if (str[i] === "G") {
      temp.push(str[i] + "C");    // Push "GC" into temp ["GC"]
    } else if (str[i] === "C") {
      temp.push(str[i] + "G");
    } else if (str[i] === "A") {
      temp.push(str[i] + "T");
    } else if (str[i] === "T") {
      temp.push(str[i] + "A");
    }
    newArr.push(temp);            // Push temp array onto result [["GC"]]
  }
  return newArr;    // Called 3 times with GCG becomes [["GC"],["CG"],["GC"]]
}

console.log(pair("GCG"));  

The push to newArr is done at the end of each loop iteration and the final result returned at end of function. The indentation was possibly not helping understanding in your pasted code.
 
Looks like you want to build the string inside the loop and push the string to the result array.

[u/ForScale]

Hey there! Looks like /u/Volv gave you a good answer.

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