Site icon R-bloggers

Check if a Variable Exists in R

Mollie

[This article was first published on Mollie's Research Blog, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.
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.
< !-- HTML generated using hilite.me -->
> 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:
< !-- HTML generated using hilite.me -->
> "varName" %in% names(df)
[1] TRUE
> any(names(df) == "varName")
[1] TRUE

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

< !-- HTML generated using hilite.me -->
> "varName" %in% colnames(df)
[1] TRUE
> any(colnames(df) == "varName")
[1] TRUE


References

To leave a comment for the author, please follow the link and comment on their blog: Mollie's Research Blog.
R-bloggers.com offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.