あなたはいくつかのツートリアルを見るべきです
# download and read in your file from dropbox
tf <- tempfile()
library(httr)
csvpage <- GET( "https://dl.dropbox.com/u/22681355/mat.csv" )
writeBin(content(csvpage, "raw"), tf )
# import the data into R
mat <- read.csv( tf )
# note read.csv creates a data frame not a matrix
class( mat )
# create your sub object
sub <- c(123,132)
# subset the matrix..
# show all rows where V2 is equal to any of the contents of sub
mat[ mat$V2 %in% sub , ]
# access only the V7 column for rows where V2 is equal to the contents of sub
mat[ mat$V2 %in% sub , 'V7' ]
# overwrite the V7 column with MISSING
# for rows where V2 is equal to the contents of sub
mat[ mat$V2 %in% sub , 'V7' ] <- NA
# OR
# overwrite the V7 column with the value of V2 (which matched something in sub)
# for rows where V2 is equal to the contents of sub
mat[ mat$V2 %in% sub , 'V7' ] <- mat[ mat$V2 %in% sub , 'V2' ]
# OR
# overwrite the V7 column with itself plus one
# for rows where V2 is equal to the contents of sub
mat[ mat$V2 %in% sub , 'V7' ] <- mat[ mat$V2 %in% sub , 'V7' ] + 1