convert character into var name for subset

Question

I am trying to remove data frame columns by subsetting the dataframe with a list of varnames, but I am getting an error:

stones<-grep("^stat\\.mineBlock\\.minecraft\\.[a-zA-Z0-9]*?stone[a-zA-Z0-9]*?", colnames(ingame), value=TRUE, ignore.case=T, perl=T)
stones<-lapply(stones, function(x) get(x))
out<-subset(out,select=-c(stones))

stones values after running line 1 above:

> stones
[1] "stat.mineBlock.minecraft.sandstone"        "stat.mineBlock.minecraft.stone"            "stat.mineBlock.minecraft.cobblestone"      "stat.mineBlock.minecraft.cobblestone_wall"
[5] "stat.mineBlock.minecraft.stone_slab"       "stat.mineBlock.minecraft.redstone_ore"     "stat.mineBlock.minecraft.stone_stairs"     "stat.mineBlock.minecraft.glowstone"       

Error on line 3:

> out<-subset(out,select=-c(stones))
Error in -c(stones) : invalid argument to unary operator

Answer 1

Using the unary operator - on character values is not allowed.

But you could use the logical negation of %in%

out[, !names(out) %in% stones]

You may even be able to use !names(out) %in% stones as the argument to select but I'm not certain due to a lack of reproducible example. For example, this works:

subset(mtcars, select = !names(mtcars) %in% "mpg")

but it's usually much safer to go with [ subsetting.