JavaScript code to remove item from array goes wrong

Question

I'm trying to remove items from an array:

for (var i = 0; i < transformedColumns.length; i++) {
  if (data[0].indexOf(transformedColumns[i] > -1)) {                   
       delete transformedColumns[i];
  }
}

The thing I'm doing Is to check if the value in transformedColumns[i] exists in data[0] array. If It does, the value should be removed from the transformedColumns.

But when I do like above, the whole transformedColumns becomes undefined.

    for (var i = 0; i < transformedColumns.length; i++) {
        if (data[0].indexOf(transformedColumns[i] > -1)) {                   
            transformedColumns.splice(transformedColumns[i], 1);
        }
    }

This works, except that it removes a value from transformedColumns that does not exist in data[0]. Let's say that transformedColumns contains ["Item No", "Item Name", "Item State"] and data[0] contains ["Item No", Item Name"]. The only values that should be removed from transformedColumnes are Item No and Item Name, not Item State.

What am I doing wrong?

delete: "The delete operator removes a property from an object", Array.prototype.splice(start, deleteCount): "start : Index at which to start changing the array", "deleteCount: An integer indicating the number of old array elements to remove" — Andreas
– Andreas, Commented Aug 14, 2017 at 7:06

Suresh Atta · Accepted Answer · 2017-08-14 07:06:10Z

1

data[0].indexOf(transformedColumns[i] > -1)

You having wrong condition statement. your condition should be

(data[0].indexOf(transformedColumns[i]) >-1 )

You are passing a condition to indexOf which fails

indexOf(transformedColumns[i] > -1)

That is the reason it is returning true for all the cases. Should work after you fix that

 for (var i = 0; i < transformedColumns.length; i++) {
        if (data[0].indexOf(transformedColumns[i]) > -1 ) {                   
            transformedColumns.splice(transformedColumns[i], 1);
        }
    }

answered Aug 14, 2017 at 7:06

Suresh Atta

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2 Comments

Jijo Cleetus Over a year ago

This is more advisable. Use splice instead of delete since delete will results in vacant space inside array.

Andreas Over a year ago

.splice(transformedColumns[i], 1) is still wrong. The first parameter of .splice() is an index and not a string.

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