# Check if a Variable Exists in R

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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

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