JavaScript indexOf() Method giving -1 when decimal value is present in array

Question

I'm having some trouble with the JavaScript indexOf() Method. I have an array...

      pointLatArray = new Array();

When I try to get the index of a variable that I know is present in the array it returns -1, which I know normally indicates to the value not being found. When my code is as follows..

      setlat = 52.6688391881732;
      pointArrayIndex = pointLatArray.indexOf(setlat);
      console.log(setlat + " " + pointLatArray[8] + " " + pointArrayIndex);

I get the following logged to console.....

       04-16 12:35:31.370: D/CordovaLog(7048): 52.6688391881732 52.6688391881732 -1

However when I change the code by replacing setlat with pointLatArray[8] in the following line....

      pointArrayIndex = pointLatArray.indexOf(pointLatArray[8]);

the following gets logged to console where it displays the correct index of 8 instead of -1 as expected.......

      04-16 12:46:17.230: D/CordovaLog(8497): 52.6688391881732 52.6688391881732 8

Is it because I'm using such a long decimal set as the variable setlat? If so, or for what ever reason if anyone could suggest a fix I would appreciate it very much.

Many thanks

score 2 · Accepted Answer · edited May 23 '17 at 11:57

2

Strict comparison for double numbers is not a good idea. Probably what you observe here is rounding error. Although the numbers seem to be the same to you they may differ by a small epsylon.

One option I see is to use custom indexOf function using epsylon comparison(i.e. allow numbers to differ by a small value. For instance 0.000000000001 or 1e-12).

edited May 23 '17 at 11:57

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answered Apr 16 '13 at 11:52

Ivaylo Strandjev

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Ok, cheers, so what would my alternative be as I'm trying to get the index of a latitude value within the array? – hotshots Apr 16 '13 at 11:54
sorry I was just searching for the right link. Take a look at my last sentence. – Ivaylo Strandjev Apr 16 '13 at 11:55
Thanks I'll have a look at there now and see can I get something from it. – hotshots Apr 16 '13 at 12:09

JavaScript indexOf() Method giving -1 when decimal value is present in array

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