Store a table row index as an array index

Question

There a simple function:

selected_row = []; // global scope

function toggleRowNumber(rowIndex) {
  if(selected_row[rowIndex]) selected_row.splice(rowIndex, 1);
  else selected_row[rowIndex] = 1; 
}

usage

toggleRowNumber(50000); // click the row - write the index
toggleRowNumber(50000); // click the row again - remove the inxed

alert(selected_row.length);

50001 OK

Delightful feature!

So is there a way to direct write|read an index without any searchin/looping? And without this huge feat as decribed above.

Thanks.

Actually it alerts 50000 which is a correct value. What did you expect? — Teemu
– Teemu, Commented Jul 29, 2013 at 6:19
Yes, 50000. I expect 0 after splice. It just like php does. $arr[50000] = 1; print sizeof($arr); // output 1 — kostya
– kostya, Commented Jul 29, 2013 at 8:41
Well, JS and PHP are different laguages. When splice shortens an array with length of 50001 by one, I'd expect the new length to be 50000 rather than 0... — Teemu
– Teemu, Commented Jul 29, 2013 at 8:45

Pablo Francisco Pérez Hidalgo · Accepted Answer · 2013-07-29 07:05:16Z

0

If I understoold correctly, you want to store and index where you can check/set whether an item is selected or not. If that is the case, you are looking for a "key - value" data structure. Then, why not use a map?

var selected_row = {};

function toggleRowNumber(rowIndex) {
if(selected_row[rowIndex]) selected_row[rowIndex] = 0; //or = undefined;
else selected_row[rowIndex] = 1; 
}

That is better because hash map will save you time and space.

Space becuase you are not storing hundreds of 'undefined' values in a vector.
Time because, hash function used to access elements is pretended to hit the right position in many cases.

edited Jul 29, 2013 at 7:05

answered Jul 29, 2013 at 6:59

Pablo Francisco Pérez Hidalgo

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8 Comments

Teemu Over a year ago

I think undefineds are not actually saved in an array, rather they are evaluated when reading the array. But time seems to be a keyword here...

kostya Over a year ago

Thanks for reply. Should I kill elem at all to loop through only existentse as sush?

kostya Over a year ago

Imagine table with huge number of rows. Couple of rows selected. User clicked another. To deselect prevously selected ones I need loop all table to clear highlight class. But with selected_rows collection all I need is to check number of selected rows and toggle class just for them. So I found stackoverflow.com/questions/6295087/remove-item-from-object

Pablo Francisco Pérez Hidalgo Over a year ago

Using a map (map = new Object() or map = {}; )the only think you have to do is to try to access to the element. Initially, for any key, its value is undefined. If you toggle one element on: map[rowIndex] = 1

kostya Over a year ago

Thanks, I have managed with this but obj give me another silly question. In order to select a range of table rows I need to know the last (and probably the first) row added to selection. In array it's simply, the last: arr(arr.length-1) but objects goig around impossibilities sort them out. In practice it works as expected: last added item take last place in collection. But to get that last index I was forced to write a ridiculous code: for(var lastIndex in selected_row){}; since .length property does nod work. How it could be done in humanly way?

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