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Convert data to factors


to_factor(x, ...)

# S3 method for class 'numeric'
to_factor(x, labels_to_levels = TRUE, verbose = TRUE, ...)

# S3 method for class 'data.frame'
  select = NULL,
  exclude = NULL,
  ignore_case = FALSE,
  append = FALSE,
  regex = FALSE,
  verbose = TRUE,



A data frame or vector.


Arguments passed to or from other methods.


Logical, if TRUE, value labels are used as factor levels after x was converted to factor. Else, factor levels are based on the values of x (i.e. as if using as.factor()).


Toggle warnings.


Variables that will be included when performing the required tasks. Can be either

  • a variable specified as a literal variable name (e.g., column_name),

  • a string with the variable name (e.g., "column_name"), or a character vector of variable names (e.g., c("col1", "col2", "col3")),

  • a formula with variable names (e.g., ~column_1 + column_2),

  • a vector of positive integers, giving the positions counting from the left (e.g. 1 or c(1, 3, 5)),

  • a vector of negative integers, giving the positions counting from the right (e.g., -1 or -1:-3),

  • one of the following select-helpers: starts_with(), ends_with(), contains(), a range using : or regex(""). starts_with(), ends_with(), and contains() accept several patterns, e.g starts_with("Sep", "Petal").

  • or a function testing for logical conditions, e.g. is.numeric() (or is.numeric), or any user-defined function that selects the variables for which the function returns TRUE (like: foo <- function(x) mean(x) > 3),

  • ranges specified via literal variable names, select-helpers (except regex()) and (user-defined) functions can be negated, i.e. return non-matching elements, when prefixed with a -, e.g. -ends_with(""), -is.numeric or -(Sepal.Width:Petal.Length). Note: Negation means that matches are excluded, and thus, the exclude argument can be used alternatively. For instance, select=-ends_with("Length") (with -) is equivalent to exclude=ends_with("Length") (no -). In case negation should not work as expected, use the exclude argument instead.

If NULL, selects all columns. Patterns that found no matches are silently ignored, e.g. extract_column_names(iris, select = c("Species", "Test")) will just return "Species".


See select, however, column names matched by the pattern from exclude will be excluded instead of selected. If NULL (the default), excludes no columns.


Logical, if TRUE and when one of the select-helpers or a regular expression is used in select, ignores lower/upper case in the search pattern when matching against variable names.


Logical or string. If TRUE, recoded or converted variables get new column names and are appended (column bind) to x, thus returning both the original and the recoded variables. The new columns get a suffix, based on the calling function: "_r" for recode functions, "_n" for to_numeric(), "_f" for to_factor(), or "_s" for slide(). If append=FALSE, original variables in x will be overwritten by their recoded versions. If a character value, recoded variables are appended with new column names (using the defined suffix) to the original data frame.


Logical, if TRUE, the search pattern from select will be treated as regular expression. When regex = TRUE, select must be a character string (or a variable containing a character string) and is not allowed to be one of the supported select-helpers or a character vector of length > 1. regex = TRUE is comparable to using one of the two select-helpers, select = contains("") or select = regex(""), however, since the select-helpers may not work when called from inside other functions (see 'Details'), this argument may be used as workaround.


A factor, or a data frame of factors.


Convert variables or data into factors. If the data is labelled, value labels will be used as factor levels. The counterpart to convert variables into numeric is to_numeric().


Factors are ignored and returned as is. If you want to use value labels as levels for factors, use labels_to_levels() instead.

Selection of variables - the select argument

For most functions that have a select argument (including this function), the complete input data frame is returned, even when select only selects a range of variables. That is, the function is only applied to those variables that have a match in select, while all other variables remain unchanged. In other words: for this function, select will not omit any non-included variables, so that the returned data frame will include all variables from the input data frame.


#> 'data.frame':	150 obs. of  5 variables:
#>  $ Sepal.Length: Factor w/ 35 levels "4.3","4.4","4.5",..: 9 7 5 4 8 12 4 8 2 7 ...
#>  $ Sepal.Width : Factor w/ 23 levels "2","2.2","2.3",..: 15 10 12 11 16 19 14 14 9 11 ...
#>  $ Petal.Length: Factor w/ 43 levels "1","1.1","1.2",..: 5 5 4 6 5 8 5 6 5 6 ...
#>  $ Petal.Width : Factor w/ 22 levels "0.1","0.2","0.3",..: 2 2 2 2 2 4 3 2 2 1 ...
#>  $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...

# use labels as levels
#>  num [1:100] 2 2 1 2 2 2 2 2 NA 2 ...
#>  - attr(*, "label")= chr "carer's level of education"
#>  - attr(*, "labels")= Named num [1:3] 1 2 3
#>   ..- attr(*, "names")= chr [1:3] "low level of education" "intermediate level of education" "high level of education"
#> [1] intermediate level of education intermediate level of education
#> [3] low level of education          intermediate level of education
#> [5] intermediate level of education intermediate level of education
#> 3 Levels: low level of education ... high level of education