How to Handle “undefined columns selected” in R

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One of the most common errors that you’ll encounter in R is:

undefined columns selected

This error occurs when you try to select a subset of a data frame and forget to add a comma.

For example, suppose we have the following data frame in R:

#create data frame with three variables
data #view DataFrame
data

  var1 var2 var3
1    0    5    2
2    4    5    7
3    2    7    9
4    2    8    9
5    5    9    7

Now suppose we attempt to select all rows where var1 is greater than 3:

data[data$var1>3]

Error in `[.data.frame`(data, data$var1 > 3) : undefined columns selected

We receive an error because we forgot to add a comma after the 3. Once we add the comma, the error will go away:

data[data$var1>3, ]

  var1 var2 var3
2    4    5    7
5    5    9    7

The reason you need to add a comma is because R uses the following syntax for subsetting data frames:

data[rows you want, columns you want]

If you only type data[data$var1>3], then you’re telling R to return the rows where var1>3, but you’re not telling R which columns to return.

By using data[data$var1>3, ], you’re telling R to return the rows where var1>3 and all of the columns in the data frame. An equivalent command would be data[data$var1>3, 1:3].

data[data$var1>3, 1:3]

  var1 var2 var3
2    4    5    7
5    5    9    7

Notice that this command returns the same subset of data as before.

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