Override [.data.frame to drop unused factor levels by default...

What is the R equivalent for Python's .cat.codes, which converts categorical variable to integer...

How to operate two variables with one factor in R...

Does plyr skip missing levels of a factor [that is the grouping variable]?...

How not to drop factor levels in R cross tabulated tables?...

Updating factor levels while filtering R data.frames...

Specify a "too large" level when converting numeric to factor in R...

In R, how can I access the first element of each level of a factor?...

R: Merging factor levels and creating sum in merged columns...

Changes in factors over time in R...

R: Make new vector correlating to a specified level in a factor...

Factor, levels, and original values...

Compare the levels of two factors...

How to convert factor levels to list, in R...

Best way in R to pick which level is the base category for a factor in an lm regression...

Exclude unused factor levels in each facet in ggplot...

Assign data to levels produced by cut (R)...

R - Obtain the connection between the numeric values and the level labels in a factor...

values don't match level in R...

Why removing a variable in an Anova containing factors in R doesn't reduce degree of freedom?...

How to show all the values in each level in r?...

Subset data frame to include only levels of one factor that have values in both levels of another fa...

Create a new level column based on unique row sets...

modifying levels in factor variable using ifelse...

Make a new variable with selected levels of another variable...

R: GLM: factor level not present in data set, but I still want coefficient...

R: Why am I not getting type or class "factor" after converting columns to factor?...

Convert a matrix from mode A to mode B...

Creating a logical variable out of a factor variable in R...

How to make the levels of a factor in a data frame consistent across all columns?...