Deleting first array element

Question

I have been trying to delete specific parts of an array, and I thought I had it working. But I cannot figure out why I cannot delete the first record.

If I set arrayToDelete to 67(representing the first element of 2nd array), or 9(representing the first element of 3rd array)...it works as I expected. But if I change arrayToDelete to 7(representing the first element of 1st array), it doesn't remove that one.

Where am I going wrong?

var mainArray = [];
var a = [7,"red","Q","gtgtg"];
mainArray.push(a);
var b = [67,"blue","s","ghft"];
mainArray.push(b);
var c = [9,"green","t","rtryt"];
mainArray.push(c);
var pickle = JSON.stringify(mainArray);
console.log("starting array - "+pickle);
console.log("starting array length - "+mainArray.length);

var arrayToDelete = "67";

var getLoc = "";

// Get position of array where first value is "1"
for (var i = 0; i < mainArray.length; i++) {
    //console.log(mainArray[i][0]);
    if(mainArray[i][0] == arrayToDelete){
        //console.log("array number "+i);
        getLoc = i;
    }
}
console.log("that number was spotted in position - "+getLoc);
//Delete from
if(getLoc != "" && getLoc != "-1"){
    mainArray.splice(getLoc, 1);  
}
var pickle2 = JSON.stringify(mainArray);
console.log("Array after removal - "+pickle2);
console.log("ending array length - "+mainArray.length);

Jan Chimiak · Accepted Answer · 2021-02-26 12:40:39Z

5

Your error is in getLoc != "". This is false for getLoc === 0.

I know js is not a strong-typed language, but you'll be better of if you write with strong-typed equality checks ===

See e.g. this article for more insights on the subject http://www.sitepoint.com/borrowing-techniques-strongly-typed-languages-javascript/ and it's always a good choice to run your code through a static code analyzer (e.g. http://jslint.com or http://jshint.com).

edited Feb 26, 2021 at 12:40

answered Feb 13, 2016 at 16:19

Jan Chimiak

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Comments

Rodney Salcedo · Accepted Answer · 2016-02-13 16:49:33Z

2

Add console.log(getLoc != "") before //Delete from, and you will see printed false when getLoc=0.

Change

console.log("that number was spotted in position - "+getLoc);
//console.log(getLoc != "")
//Delete from
if(getLoc != "" && getLoc != "-1"){
    mainArray.splice(getLoc, 1);  
}

by

console.log("that number was spotted in position - "+getLoc);
//console.log(getLoc !== "")
//Delete from
if(getLoc !== "" && getLoc != "-1"){
    mainArray.splice(getLoc, 1);  

}

edited Feb 13, 2016 at 16:49

answered Feb 13, 2016 at 16:37

Rodney Salcedo

1,26419 silver badges25 bronze badges

4 Comments

Jeremy J Starcher Over a year ago

Upvote for telling the OP how to discover the problem on their own.

Rodney Salcedo Over a year ago

@JeremyJStarcher Do you think is better to show the error than solve the issue?

Jeremy J Starcher Over a year ago

Both, of course. I was just saying that I like educational answers that, hopefully, teach people how to do their own debugging.

Rodney Salcedo Over a year ago

I agree @JeremyJStarcher

Viktor Molokostov · Accepted Answer · 2016-07-20 20:27:53Z

1

Functional approach might be much more readable in this case:

mainArray = mainArray.filter(arr => arr[0] !== arrayToDelete);

edited Jul 20, 2016 at 20:27

answered Feb 13, 2016 at 16:19

Viktor Molokostov

6437 silver badges15 bronze badges

1 Comment

Jeremy J Starcher Over a year ago

This shares the code-fault of the original != vs !==

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