sjmisc (version 2.3.0)

to_value: Convert factors to numeric variables

Description

This function converts (replaces) factor values with the related factor level index number, thus the factor is converted to a numeric variable.

Usage

to_value(x, ..., start.at = NULL, keep.labels = TRUE)

Arguments

x

A vector or data frame.

...

Optional, unquoted names of variables. Required, if x is a data frame (and no vector) and only selected variables from x should be processed. You may also use functions like : or dplyr's select_helpers. The latter must be stated as formula (i.e. beginning with ~). See 'Examples' or package-vignette.

start.at

Starting index, i.e. the lowest numeric value of the variable's value range. By default, this argument is NULL, hence the lowest value of the returned numeric variable corresponds to the lowest factor level (if factor levels are numeric) or to 1 (if factor levels are not numeric).

keep.labels

Logical, if TRUE, former factor levels will be added as value labels. For numeric factor levels, values labels will be used, if present. See 'Examples' and set_labels for more details.

Value

A numeric variable with values ranging either from start.at to start.at + length of factor levels, or to the corresponding factor levels (if these were numeric). Or a data frame with numeric variables, if x was a data frame.

Examples

data(efc)
test <- to_label(efc$e42dep)
table(test)

table(to_value(test))
hist(to_value(test, start.at = 0))

# set lowest value of new variable to "5".
table(to_value(test, start.at = 5))

# numeric factor keeps values
dummy <- factor(c("3", "4", "6"))
table(to_value(dummy))

# do not drop unused factor levels
dummy <- ordered(c(rep("No", 5), rep("Maybe", 3)),
                 levels = c("Yes", "No", "Maybe"))
to_value(dummy)

# non-numeric factor is converted to numeric
# starting at 1
dummy <- factor(c("D", "F", "H"))
table(to_value(dummy))

# for numeric factor levels, value labels will be used, if present
dummy1 <- factor(c("3", "4", "6"))
dummy1 <- set_labels(dummy1, labels = c("first", "2nd", "3rd"))
dummy1
to_value(dummy1)

# for non-numeric factor levels, these will be used.
# value labels will be ignored
dummy2 <- factor(c("D", "F", "H"))
dummy2 <- set_labels(dummy2, labels = c("first", "2nd", "3rd"))
dummy2
to_value(dummy2)


# easily coerce specific variables in a data frame to numeric
# and keep other variables, with their class preserved
data(efc)
efc$e42dep <- as.factor(efc$e42dep)
efc$e16sex <- as.factor(efc$e16sex)
efc$e17age <- as.factor(efc$e17age)

# convert back "sex" and "age" into numeric
to_value(efc, e16sex, e17age)