What is the general procedure or general rules for grouping factor levels?
10256
Principled way of collapsing categorical variables with many levels?
75677
Dealing with new Factor Levels in a Regression in R
61694
How to get an "overall" p-value and effect size for a categorical factor in a mixed model (lme4)?
25535
Categorical Principal Component Analysis - using Count, Continuous, Ordinal variables together
84327
How to make a traditional division
127581
Factor analysis of questionnaires composed of Likert items
64536
How to correctly treat multiple data points per each subject
42578
If a factor variable is to be dropped in model selection, should all levels be dropped simultaneously? If so, why?
50580
Suppressing reduction in fraction box size in multi-level fractions
132510
From exp (coefficients) to Odds Ratio and their interpretation in Logistic Regression with factors
24411
Aggregate / summarize multiple variables per group (e.g. sum, mean)
154146
How are simple groups the building blocks?
55747
Grouping functions (tapply, by, aggregate) and the *apply family
142378
Levels: how do they work?
125960
Factor groups of matrices
149518
Adding counts of a factor to a dataframe
132210
How to assign a counter to a specific subset of a data.frame which is defined by a factor combination?