What does the "Undefined Columns Selected R error" mean when using the PPRL package?

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The "Undefined Columns Selected R error" in the PPRL package means that there is an issue with the column names or indexes of the dataset you are using. This error occurs when you try to access a column that does not exist in the dataset or when you are using an incorrect column name or index. To fix this error, you need to make sure that the column names and indexes are correct and match the ones in your dataset.