[R] Using vectorization instead of for loop for performing a calculation efficiently

Peter Wilkinson pwilkinson at videotron.ca
Sun Apr 2 01:52:55 CEST 2006

 I am trying to write an efficient function that will do the following:

Given an nxm matrix, 10 rows (observations) by 10 columns (samples) 
for each row, test of all values in the row are greater than a value k
If all values are greater than k, then set all values to NA (or something),
Return an nxm matrix with the modified rows.

If I do this with a matrix of 20,000 rows, I will be waiting until Christmas
for it to finish:

For rows in Matrix:
	if rows < filter
		set all elements in rows to NA   (or something)
		do nothing
Return the matrix with the modified rows

I don’t know how to code this properly. The following:

If (sum(ifelse(nvector>filter,1,0) == 0 ) )

Tells me if any row has at least 1 value above the filter. How do I get rid
of the 'outer' loop?



Peter Wilkinson
Senior Bioinformatician / Programmer-Analyst
National Immune Monitoring Laboratory
tel: (514)-343-7876

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