# Extracting specific data points from a matrix

Hello Forum,

I have a matrix (table9) and I want to extract specific data points such that I also copy values in nearby columns (to table8),

for example, in image attached you can see that data from table9 column 0 are picked and corresponding values from column 1 and 2 are also copied.

I can do it for a 1D wave, picking values in column between 7 and 12

Extract /o SourceWave , DestWave , SourceWave >=7 && SourceWave <=12

Now I have a matrix, I want to get the nearby data as well,

There might be a faster way, but this one will work:

// make some data
make/N=(20,3) w
w[][0] = 6 + enoise(6)
w[][1] = 750 + enoise(50)
w[][2] = 350 + enoise(20)

MatrixOP/O index = col(w,0)
index = index[p] > 7 && index[p] < 12 ? p : NaN
Wavetransform zapNaNs index
Make/O/N=(numpnts(index),3) output = w[index[p]][q]

And a different way to do, haven't tested speed:

Function extractRows(Wave matrix2d, String newwname, Variable upper, Variable lower)
Duplicate/FREE/R=[][0] matrix2d, c0
Extract/INDX/FREE c0, indx, (c0 > lower) && (c0 < upper)
Make/N=(numpnts(indx), DimSize(matrix2d,1))/O \$newwname/WAVE=w
w = matrix2d[indx[p]][q]
end

@ChrLie That suggestion is very elegant. I used to do this by setting each row as NaN and then use a separate function to split the matrix, zapnans in each and then put it back together. No more!

... and when you get your hands on IP9 you might want to check the implementation of zapNaNs() in MatrixOP  :)