Removing a column from a matrix

Question

I'm a bit new to R and wanting to remove a column from a matrix by the name of that column. I know that X[,2] gives the second column and X[,-2] gives every column except the second one. What I really want to know is if there's a similar command using column names. I've got a matrix and want to remove the "sales" column, but X[,-"sales"] doesn't seem to work for this. How should I do this? I would use the column number only I want to be able to use it for other matrices later, which have different dimensions. Any help would be much appreciated.

Answer 1

I'm not sure why all the answers are solutions for data frames and not matrices.

Per @Sotos's and @Moody_Mudskipper's comments, here is an example with the builtin state.x77 data matrix.

dat <- head(state.x77)
dat
#>            Population Income Illiteracy Life Exp Murder HS Grad Frost   Area
#> Alabama          3615   3624        2.1    69.05   15.1    41.3    20  50708
#> Alaska            365   6315        1.5    69.31   11.3    66.7   152 566432
#> Arizona          2212   4530        1.8    70.55    7.8    58.1    15 113417
#> Arkansas         2110   3378        1.9    70.66   10.1    39.9    65  51945
#> California      21198   5114        1.1    71.71   10.3    62.6    20 156361
#> Colorado         2541   4884        0.7    72.06    6.8    63.9   166 103766

# for removing one column
dat[, colnames(dat) != "Area"]
#>            Population Income Illiteracy Life Exp Murder HS Grad Frost
#> Alabama          3615   3624        2.1    69.05   15.1    41.3    20
#> Alaska            365   6315        1.5    69.31   11.3    66.7   152
#> Arizona          2212   4530        1.8    70.55    7.8    58.1    15
#> Arkansas         2110   3378        1.9    70.66   10.1    39.9    65
#> California      21198   5114        1.1    71.71   10.3    62.6    20
#> Colorado         2541   4884        0.7    72.06    6.8    63.9   166

# for removing more than one column
dat[, !colnames(dat) %in% c("Area", "Life Exp")]
#>            Population Income Illiteracy Murder HS Grad Frost
#> Alabama          3615   3624        2.1   15.1    41.3    20
#> Alaska            365   6315        1.5   11.3    66.7   152
#> Arizona          2212   4530        1.8    7.8    58.1    15
#> Arkansas         2110   3378        1.9   10.1    39.9    65
#> California      21198   5114        1.1   10.3    62.6    20
#> Colorado         2541   4884        0.7    6.8    63.9   166

#be sure to use `colnames` and not `names`
names(state.x77)
#> NULL

^{Created on 2020-06-27 by the reprex package (v0.3.0)}