[R] Fastest way to extract rows of smaller matrix many times by index to make larger matrix? and multiply columsn of matrix by vector

Leonard Mada |eo@m@d@ @end|ng |rom @yon|c@eu
Tue Sep 14 15:46:46 CEST 2021

Hello Nevil,

you could test something like:

# the Matrix
m = matrix(1:1000, ncol=10)
m = t(m)

# Extract Data
idcol = sample(seq(100), 100, TRUE); # now columns
for(i in 1:100) {
     m2 = m[ , idcol];
m2 = t(m2); # transpose back

It may be faster, although I did not benchmark it.

There may be more complex variants. Maybe it is warranted to try for 
10^7 extractions:

- e.g. extracting one row and replacing all occurrences of that row;




It seems I cannot extract digested mail anymore. I hope though that the 
message is processed properly.

More information about the R-help mailing list