Hi,

I am not sure whether Nick wants to find out the fraction of the required illuminance level each point achieves (that is what Andrew calculates) or the fraction of (the amount of) points that meet the criteria. For the second you have three steps involved:

1) filter the input according to you treshold (300lx)

2) count the value meeting the criteria

3) divide by the total number of points and multiply by 100 to get a percentage

This can be translated like into:

cat test.dat | rcalc -e '$1=1; $2=if($1-299,1,0)' | total | rcalc -e '$1=100*$2/$1'

The first step, rcalc, takes one column (you can adapt this according to your input file) and writes out two columns. The first is set to 1 for any input, the second is set to one for inputs > 2990 and to 0 for anything below.

The second step, total, sums up the result of the first step. You get the sums of two columns - two numbers, the first being the amount of original input values, the second the amount of values that are above 299.

The third step, rcalc again, divides the number of points meeting the criteria by the total number of values and multiplies this by 100. This results in the percentage of values meeting the criteria.

There are quicker ways to achieve this, but I wanted a transparent format that one can explain. Hope this helps, cheers

Lars.