[R] Drop column from a data frame

[John Sorkin]

I am trying to drop a column of a data frame. The code below attempts to drop a numeric column (which does not work but gives no error or warning) and a factor column (which does not work but gives an error).
I would appreciate someone telling me why my code does not work, and suggesting code that will work.
Thanks,
John

rm(dfxyz,dfxz,dfxy)

# create the data frame.
dfxyz <- data.frame(x=1:10,y=11:20,z=factor(c(rep(0,5),rep(1,5))))
dfxyz

names(dfxyz)

# try to drop y column
# does not work, does not produce error message
dfxz <- dfxyz[,-(dfxyz$y)]
dfxz

# try to drop z column
# does not work, produces error message:
# In Ops.factor(df$z) : - not meaningful for factors
dfxy <- dfxyz[,-dfxyz$z]
dfxy



John David Sorkin M.D., Ph.D.
Chief, Biostatistics and Informatics
University of Maryland School of Medicine Division of Gerontology
Baltimore VA Medical Center
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
(Phone) 410-605-7119
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