Consider the following dataframe:
df <- data.frame(x=1:5, y=6:10, z=11:15, a=16:20)
I can select a column using just the name:
df2 <- subset (df, select = x)
Or I can select it passing the name as a string:
df2 <- subset (df, select = c("x"))
I can delete a column by passing just the name:
df2 <- subset (df, select = -x)
But I cannot delete it passing the name as string:
df2 <- subset (df, select = -c("x"))
As it returns the error:
Error in -c("x") : invalid argument to unary operator
Why?