Katie C
2008-Mar-08 05:17 UTC
[R] Deleting rows satisfying a certain condition (sum of some colums>2)
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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jim holtman
2008-Mar-08 14:08 UTC
[R] 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 criteriameet.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; > > -- > View this message in context: http://www.nabble.com/Deleting-rows-satisfying-a-certain-condition-%28sum-of-some-colums%3E2%29-tp15911408p15911408.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >-- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem you are trying to solve?