Rounding percentages for poll results

[bpp198]

I am having trouble getting my percentages to add up to 100%.

When I calculate the percentages from a poll, I want them rounded to a whole percentage. However, due to the scientific way php rounds .5% values (ie. evens are rounded up and odds rounded down (or the other way round)), this can result in the percentages adding up to a number other than 100%.

Has anyone found a way to combat this?

Thanks,
Benji.

[spxdcz]

In my experience, the best way to do this is:

Loop over each result, EXCEPT the last value. You can round each result in this loop, as normal. In the loop, also keep a variable which holds the cumulative value of each rounded result, e.g. $cumulative = $cumulative + $rounded_percentage.

For the last result, rather than rounding the value, just use (100 - $cumulative). This way, you'll always get 100 as the total.

The only problem with this method is that it is often slightly misleading - if you had 3 results, each with one vote, then your percentages would be 34%, 34% and 32%, which is obviously a bit misleading...

[cordex]

Which is why you always have a visible margin of error.

[bpp198]

Thanks for the replies.

I loop through the results from a MySQL database and am displaying in a webpage using PHP. How do I know when I am on the last result? Do I simply have to test using mysql_num_rows($result_id) and then count the number of rows already printed, or is there a simple way?

Cheers,
Benji.

[bpp198]

Anybody know of any other solutions to this problem? The above solution works okay, but we have polls with few participants, so if the last answer has no votes, it is occasionally given a 1% which looks a bit strange to say the least.

Benji.