Dan --

Don't quite understand exactly what you're trying to do, but two Excel 2003
functions should work nicely: =PERCENTILE, and =PERCENTILERANK. An example:

=PERCENTILE(A1:A9999,0.25)

It sounds like you have different classes of results, classed by your index
number. If that's correct and the data is fairly static, you might sort them
first. If not, then we can play with a better formula that takes those
classes into account.

HTH

"Dan" wrote:

Hi, I have a large series of numbers saved in one column
[34,5,21,98,34,3,432,55,27,90,1125,......]. These data are indexed, e.g. by
[1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,......N] which are in another column.

Basically I am calculating the 25% percentiles for numbers indexed "1", "2",
"3",...., "N" respectivelly. There are a lot of numbers with a big uplimit of
index "N" so that selecting numbers of each index manually is not easy.

In another word, if N = 9999, then I need to calculate N 25% percentiles
with one for each indexed number class. That is it. Thansk for any input!








Thanks a lot!