[R] matrix looping accessing previous column

Hi, I have a matrix with numbers and character. I want to evaluate each cell and change the value of the cell before it depending on the evaluation. My evaluation: if a cell had the word down change the cell preceding it to a negative number by multiplying that value by a -1. I am have trouble

Re: [R] matrix looping accessing previous column

Try this: x V1 V2 V3 V4 1 PROBE 1 2.5 UP 2 PROBE 2 1.0 UP 3 PROBE 3 1.4 DOWN 4 PROBE 4 2.0 UP 5 PROBE 5 1.3 DOWN x$V3[which(x$V4 == DOWN) - 1] - x$V3[which(x$V4 == DOWN) - 1] * -1 On Mon, Dec 27, 2010 at 4:11 PM, R_novice kaso...@battelle.org wrote: Hi, I have a matrix

Re: [R] matrix looping accessing previous column

Thank you for the quick response :-). I've applied your suggestion to my code, but I still receive an error: CEM1_PARTIAL$V3[which(CEM1_PARTIAL$V4 == DOWN) - 1] - CEM1_PARTIAL$V3[which(CEM1_PARTIAL$V4 == DOWN) - 1] * -1 Warning message: In Ops.factor(CEM1_PARTIAL$V3[which(CEM1_PARTIAL$V4 ==

Re: [R] matrix looping accessing previous column

Convert your column to numeric: CEM1_PARTIAL$V3 - as.numeric(as.character(CEM1_PARTIAL$V3)) On Mon, Dec 27, 2010 at 4:28 PM, R_novice kaso...@battelle.org wrote: Thank you for the quick response :-). I've applied your suggestion to my code, but I still receive an error:

Re: [R] matrix looping accessing previous column

That just converts my values in V3 to NA -- View this message in context: http://r.789695.n4.nabble.com/matrix-looping-accessing-previous-column-tp3165308p3165340.html Sent from the R help mailing list archive at Nabble.com. __

Re: [R] matrix looping accessing previous column

Using which() improves my code, but now I'm receiving some data.frame error and still does not convert the values to negative. #TAKE PART OF MATRIX CEM1_PARTIAL - CEM1[1:10,1:10] #CEM1_PARTIAL=apply(CEM1_PARTIAL,2,as.character) #CEM1_PARTIAL - as.numeric(as.character(CEM1_PARTIAL))