Deleting rows satisfying a certain condition (sum of some colums>2)
Here is a way of doing it. You check to see which ones meet the criteria and then delete them.
# create indices of columns to match first.col <- seq(1, to=ncol(SS) - 2) sec.col <- seq(3, to=ncol(SS)) # determine rows that met criteria meet.crit <- apply(SS, 1, function(.row) any((.row[first.col] + .row[sec.col]) > 2)) cbind(SS, meet.crit) # show which ones meet criteria
meet.crit [1,] 2 2 2 2 1 [2,] 2 2 1 2 1 [3,] 2 2 1 1 1 [4,] 2 2 0 2 1 [5,] 2 2 0 1 1 [6,] 2 2 0 0 0 [7,] 1 2 2 2 1 [8,] 1 2 1 2 1 [9,] 1 2 1 1 1 [10,] 1 2 0 2 1 [11,] 1 2 0 1 1 [12,] 1 2 0 0 0 [13,] 1 1 2 2 1 [14,] 1 1 1 2 1 [15,] 1 1 1 1 0 [16,] 1 1 0 2 1 [17,] 1 1 0 1 0 [18,] 1 1 0 0 0
SS[!meet.crit,] # remove them
[,1] [,2] [,3] [,4] [1,] 2 2 0 0 [2,] 1 2 0 0 [3,] 1 1 1 1 [4,] 1 1 0 1 [5,] 1 1 0 0
On Sat, Mar 8, 2008 at 12:17 AM, Katie C <katie.cheon at gmail.com> wrote:
I have a huge matrix and need to delete certain rows. What I need to do is:
1.In each row, calculate the sum of jth column and (J+2)th column
2. If the sum is greater than 2 then that row needs to be deleted.
I have a sample matrix and my codes here. It does remove some rows but when
it does, it skips the next row and each time it deletes a row, the dimension
changes so it gets out of bound. I tried to fix those problems but it did
not work. Any suggestions please? Thank you.
S1=c(2,2,2,2,2,2,1,1,1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2,2,2,
1,1,1,1,1,1,2,1,1,0,0,0,2,1,1,0,0,0,2,1,1,0,0,0,2,2,1,2,1,0,2,2,1,2,1,0,2,2,1,2,1,0);
SS=matrix(S1,nrow=18);
nr =dim(SS)[1];
nc =dim(SS)[2]/2;
nt=2;
ms=2;
for (i in 1:nr){
for (j in 1:nc){
#print(paste("Sum=",SS[i,j]+SS[i,j+nt]," ms=",ms));
if (SS[i,j]+SS[i,j+nt]> ms){
SS=SS[-i,]
nr=dim(SS)[1] #this doesn't update nr in the outer for loop. why?
print(nr) }
}
# i=i-1 #this doesn't help to avoid skipping rows
}
SS;
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