Hi
I would like to get help in combining two matrices. Here is my example: A <- 1:20 B <- matrix(A,nrow=5,ncol=4) # B is a numerical matrix C <- B<7 C[4,4] <- TRUE # C is a logical matrix # if I combine A and C, I get a vector D1 <- A[C==TRUE] D1 D2 <- A[C==FALSE] D2 I want to get a matrix with the same dimensions as matrix A. At the coordinates given by the vector D1, I want to retain the values in matrix A. At the locations in D2, I want a zero value. I want to know if I can do this without using any loops. Thanks, Vivek [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see 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. |
The result that I want to get is this:
for (i in 1:5) { for (j in 1:4) { B[i,j] <- ifelse(C[i,j]==FALSE,0,B[i,j]) } } I would like to know if I can do this without loops. Den lör 5 sep. 2020 kl 20:18 skrev Vivek Sutradhara <[hidden email]>: > Hi > I would like to get help in combining two matrices. Here is my example: > A <- 1:20 > B <- matrix(A,nrow=5,ncol=4) > # B is a numerical matrix > C <- B<7 > C[4,4] <- TRUE > # C is a logical matrix > # if I combine A and C, I get a vector > D1 <- A[C==TRUE] > D1 > D2 <- A[C==FALSE] > D2 > > I want to get a matrix with the same dimensions as matrix A. At the > coordinates given by the vector D1, I want to retain the values in > matrix A. At the locations in D2, I want a zero value. > I want to know if I can do this without using any loops. > Thanks, Vivek > [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see 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. |
In reply to this post by vivek
A is not a matrix. I presume you meant B. If so:
> B[!C] <- 0 > B [,1] [,2] [,3] [,4] [1,] 1 6 0 0 [2,] 2 0 0 0 [3,] 3 0 0 0 [4,] 4 0 0 19 [5,] 5 0 0 0 Cheers, Bert On Sat, Sep 5, 2020 at 11:18 AM Vivek Sutradhara <[hidden email]> wrote: > Hi > I would like to get help in combining two matrices. Here is my example: > A <- 1:20 > B <- matrix(A,nrow=5,ncol=4) > # B is a numerical matrix > C <- B<7 > C[4,4] <- TRUE > # C is a logical matrix > # if I combine A and C, I get a vector > D1 <- A[C==TRUE] > D1 > D2 <- A[C==FALSE] > D2 > > I want to get a matrix with the same dimensions as matrix A. At the > coordinates given by the vector D1, I want to retain the values in > matrix A. At the locations in D2, I want a zero value. > I want to know if I can do this without using any loops. > Thanks, Vivek > > [[alternative HTML version deleted]] > > ______________________________________________ > [hidden email] mailing list -- To UNSUBSCRIBE and more, see > 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. > [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see 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. |
Here is a way of doing it using the 'arr.ind' option in 'which'
> A <- 1:20 > B <- matrix(A,nrow=5,ncol=4) > B [,1] [,2] [,3] [,4] [1,] 1 6 11 16 [2,] 2 7 12 17 [3,] 3 8 13 18 [4,] 4 9 14 19 [5,] 5 10 15 20 > # B is a numerical matrix > C <- B<7 > C[4,4] <- TRUE > C [,1] [,2] [,3] [,4] [1,] TRUE TRUE FALSE FALSE [2,] TRUE FALSE FALSE FALSE [3,] TRUE FALSE FALSE FALSE [4,] TRUE FALSE FALSE TRUE [5,] TRUE FALSE FALSE FALSE > > # initialize a 'result' with zeros > result <- array(0, dim = dim(B)) > > # get the indices of values to replace > indx <- which(C, arr.ind = TRUE) > > result[indx] <- B[indx] > > result [1,] 1 6 0 0 [2,] 2 0 0 0 [3,] 3 0 0 0 [4,] 4 0 0 19 [5,] 5 0 0 0 > Jim Holtman *Data Munger Guru* *What is the problem that you are trying to solve?Tell me what you want to do, not how you want to do it.* On Sat, Sep 5, 2020 at 11:51 AM Bert Gunter <[hidden email]> wrote: > A is not a matrix. I presume you meant B. If so: > > > B[!C] <- 0 > > B > [,1] [,2] [,3] [,4] > [1,] 1 6 0 0 > [2,] 2 0 0 0 > [3,] 3 0 0 0 > [4,] 4 0 0 19 > [5,] 5 0 0 0 > > Cheers, > Bert > > > > > > On Sat, Sep 5, 2020 at 11:18 AM Vivek Sutradhara <[hidden email]> > wrote: > > > Hi > > I would like to get help in combining two matrices. Here is my example: > > A <- 1:20 > > B <- matrix(A,nrow=5,ncol=4) > > # B is a numerical matrix > > C <- B<7 > > C[4,4] <- TRUE > > # C is a logical matrix > > # if I combine A and C, I get a vector > > D1 <- A[C==TRUE] > > D1 > > D2 <- A[C==FALSE] > > D2 > > > > I want to get a matrix with the same dimensions as matrix A. At the > > coordinates given by the vector D1, I want to retain the values in > > matrix A. At the locations in D2, I want a zero value. > > I want to know if I can do this without using any loops. > > Thanks, Vivek > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > [hidden email] mailing list -- To UNSUBSCRIBE and more, see > > 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. > > > > [[alternative HTML version deleted]] > > ______________________________________________ > [hidden email] mailing list -- To UNSUBSCRIBE and more, see > 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. > [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see 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. |
In reply to this post by vivek
(1) Using 'C == TRUE' (when you know C is logical)
is equivalent to just plain C, only obscure. Similarly, 'C == FALSE' is more confusing than !C. (2) Consider B[C]. The rows of C have 2, 1, 1, 2, 1 TRUE. entries, so the result here *cannot* be a rectangular array. And whatever it is, it contains only the elements where C is true. (3) You probably already knew that 'ifelse' is vectorised. What you may not have realised is that it preserves array dimensions as well. > A <- cbind(c(1,2), c(3,4)) > B <- cbind(c(5,6), c(7,8)) > C <- cbind(c(FALSE,TRUE), c(TRUE,FALSE)) > ifelse(C, A, B) [,1] [,2] [1,] 5 3 [2,] 2 8 > ifelse(C, A, 0) [,1] [,2] [1,] 0 3 [2,] 2 0 Isn't it nice when the obvious code just works? On Sun, 6 Sep 2020 at 06:18, Vivek Sutradhara <[hidden email]> wrote: > Hi > I would like to get help in combining two matrices. Here is my example: > A <- 1:20 > B <- matrix(A,nrow=5,ncol=4) > # B is a numerical matrix > C <- B<7 > C[4,4] <- TRUE > # C is a logical matrix > # if I combine A and C, I get a vector > D1 <- A[C==TRUE] > D1 > D2 <- A[C==FALSE] > D2 > > I want to get a matrix with the same dimensions as matrix A. At the > coordinates given by the vector D1, I want to retain the values in > matrix A. At the locations in D2, I want a zero value. > I want to know if I can do this without using any loops. > Thanks, Vivek > > [[alternative HTML version deleted]] > > ______________________________________________ > [hidden email] mailing list -- To UNSUBSCRIBE and more, see > 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. > [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list -- To UNSUBSCRIBE and more, see 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. |
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