How the warning can be avoided:
We can get rid of this warning by firstly transforming the factor variable to a character variable and then we can transform it again to a factor variable just after adding the additional row.
Example:
R
# Create a data frame dataframe <- data.frame(team=factor(c('Alpha', 'Alpha', 'Beta', 'Beta', 'Charlie', 'Charlie', 'Charlie')), points=c(96, 91, 86, 89, 93, 87, 91)) # Convert team variable to character dataframe$team <- as.character(dataframe$team) # Insert a new row to end of data frame dataframe[nrow(dataframe) + 1,] = c('Gamma', 99) # Transform team variable back to factor dataframe$team <- as.factor(dataframe$team) # Display the data frame dataframe |
Output:
As you can see in the output, the warning, as well as the “NA” thing, have been eliminated from the dataframe. Now let’s display the structure of the modified dataframe once:
R
# Create a data frame dataframe <- data.frame(team=factor(c('Alpha', 'Alpha', 'Beta', 'Beta', 'Charlie', 'Charlie', 'Charlie')), points=c(96, 91, 86, 89, 93, 87, 91)) # Convert team variable to character dataframe$team <- as.character(dataframe$team) # Insert a new row to end of data frame dataframe[nrow(dataframe) + 1,] = c('Gamma', 99) # Transform team variable back to factor dataframe$team <- as.factor(dataframe$team) # Display the structure of the data frame str(dataframe) |
Output:
How to Fix: Invalid factor level, NA generated in R
In this article, we will be looking at the approaches with the examples to fix the error: invalid factor level, NA generated.
Such type of warning message is produced by the compiler when a programmer tries to add a value to a factor variable in R that doesn’t have any existence at the beforehand as a defined level. The complete warning message is given below:
Warning message: In `[<-.factor`(`*tmp*`, iseq, value = "C") : invalid factor level, NA generated