[R] extracting the i-th row of a matrix in a list of lists
Hi, what is the proper of of passing a missing value so I can extract the entire i-th row of a matrix (in a list of lists) without pre-computing the number of cols? For example, if I know that the matrices have 2 columns, I can do the following: set.seed(1) x0 - lapply(1:10, function(i) replicate(4, list(matrix(rnorm(10), nc=2 lapply(lapply(x0, '[[', 3), '[', i=2, j=1:2) (given that if I don't specify j, I only get the first element) but if the number of columns are variable: x1 - lapply(1:10, function(i) replicate(4, list(matrix(rnorm(100), nc=sample(c(2, 4, 5, 10), 1) what would be the value of J below? lapply(lapply(x1, '[[', 3), '[', i=2, j=J) or should I really stick with: lapply(lapply(x1, '[[', 3), function(x) x[2,]) ? Thank you very much, benilton __ R-help@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.
Re: [R] extracting the i-th row of a matrix in a list of lists
Benilton Carvalho beniltoncarva...@gmail.com writes: Hi, what is the proper of of passing a missing value so I can extract the entire i-th row of a matrix (in a list of lists) without pre-computing the number of cols? For example, if I know that the matrices have 2 columns, I can do the following: set.seed(1) x0 - lapply(1:10, function(i) replicate(4, list(matrix(rnorm(10), nc=2 lapply(lapply(x0, '[[', 3), '[', i=2, j=1:2) (given that if I don't specify j, I only get the first element) but if the number of columns are variable: x1 - lapply(1:10, function(i) replicate(4, list(matrix(rnorm(100), nc=sample(c(2, 4, 5, 10), 1) what would be the value of J below? lapply(lapply(x1, '[[', 3), '[', i=2, j=J) I think you want 'j=TRUE'. Note: all.equal( lapply(lapply(x0, '[[', 3), '[', i=2,j=TRUE), lapply(lapply(x0, '[[', 3), '[', i=2, j=1:2) ) HTH, Chuck or should I really stick with: lapply(lapply(x1, '[[', 3), function(x) x[2,]) ? Thank you very much, benilton -- Charles C. BerryDept of Family/Preventive Medicine cberry at ucsd edu UC San Diego http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901 __ R-help@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.
Re: [R] extracting the i-th row of a matrix in a list of lists
Hi Chuck, thank you *very* much! That really helped! b On 9 March 2012 17:15, cbe...@tajo.ucsd.edu wrote: Benilton Carvalho beniltoncarva...@gmail.com writes: Hi, what is the proper of of passing a missing value so I can extract the entire i-th row of a matrix (in a list of lists) without pre-computing the number of cols? For example, if I know that the matrices have 2 columns, I can do the following: set.seed(1) x0 - lapply(1:10, function(i) replicate(4, list(matrix(rnorm(10), nc=2 lapply(lapply(x0, '[[', 3), '[', i=2, j=1:2) (given that if I don't specify j, I only get the first element) but if the number of columns are variable: x1 - lapply(1:10, function(i) replicate(4, list(matrix(rnorm(100), nc=sample(c(2, 4, 5, 10), 1) what would be the value of J below? lapply(lapply(x1, '[[', 3), '[', i=2, j=J) I think you want 'j=TRUE'. Note: all.equal( lapply(lapply(x0, '[[', 3), '[', i=2,j=TRUE), lapply(lapply(x0, '[[', 3), '[', i=2, j=1:2) ) HTH, Chuck or should I really stick with: lapply(lapply(x1, '[[', 3), function(x) x[2,]) ? Thank you very much, benilton -- Charles C. Berry Dept of Family/Preventive Medicine cberry at ucsd edu UC San Diego http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901 __ R-help@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. __ R-help@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.
