Check if a Variable Exists in R

If you use attach, it is easy to tell if a variable exists. You can simply use exists to check:

>attach(df)

>exists("varName")
[1] TRUE

However, if you don't use attach (and I find you generally don't want to), this simple solution doesn't work.

> detach(df)
> exists("df$varName")
[1] FALSE

Instead of using exists, you can use in or any from the base package to determine if a variable is defined in a data frame:

> "varName" %in% names(df)
[1] TRUE
> any(names(df) == "varName")
[1] TRUE

Or to determine if a variable is defined in a matrix:

> "varName" %in% colnames(df)
[1] TRUE
> any(colnames(df) == "varName")
[1] TRUE

References

• https://stat.ethz.ch/pipermail/r-help/2009-June/202178.html
• https://stat.ethz.ch/pipermail/r-help/2011-February/267518.html