Matrix to list of matrix group by column names in R -

i have matrix 6000 columns , each column belongs 1 of 100 "groups" need. need convert matrix list 100 smaller matrices. toy example of have:

  mat = cbind(c(2,2,2),c(3,3,3),c(4,4,4),c(1,1,1))   colnames(mat) = c("2018.3 1","2018.3 2","2019.1 1","2019.2 2") 

so "group" identified last name of each colname, here there 2 groups. result need like:

list(cbind(c(2,2,2),c(4,4,4)),cbind(c(3,3,3),c(1,1,1))) 

i've been thinking , think should this:

lapply(do.call(cbind,sapply(something here find columns in each group))) 

but haven't figure out how it.

#obtain last part of each column names groups = sapply(strsplit(x = colnames(mat), split = " "), function(x) x[2])  #go through each unique column name , extract corresponding columns lapply(unique(groups), function(x) mat[,which(groups == x)]) #[[1]] #     2018.3 1 2019.1 1 #[1,]        2        4 #[2,]        2        4 #[3,]        2        4  #[[2]] #     2018.3 2 2019.2 2 #[1,]        3        1 #[2,]        3        1 #[3,]        3        1 

or

lapply(split(1:ncol(mat), sapply(strsplit(x = colnames(mat), split = " "),                                  function(x) x[2])), function(i) mat[,i]) #$`1` #     2018.3 1 2019.1 1 #[1,]        2        4 #[2,]        2        4 #[3,]        2        4  #$`2` #     2018.3 2 2019.2 2 #[1,]        3        1 #[2,]        3        1 #[3,]        3        1