Translate variables

Adrian Maldet

2019-10-08

Source: vignettes/translate.Rmd

In the following, we will explain how to use a lama-dictionary (See Creating lama-dictionaries) in order to translate data frame variables or atomic vectors (or factor objects). The main functions are: * lama_translate() and lama_translate_(): Assign new labels to variable values and turn them into ordered factors (if to_factor = TRUE). * lama_translate_all(): Apply lama_translate() on all possible columns of a data frame, if there are corresponding translations. * lama_to_factor() and lama_to_factor_(): Similar to lama_translate() and lama_translate_(), but the variables already have the right values (character or factor), but should be turned into factor variables with the factor levels given in the corresponding translations. * lama_to_factor_all(): Apply lama_to_factor() on all possible columns of a data frame, if there are corresponding translations.

The example data frame and lama-dictionary

Let df be a data frame with the following structure:

The column subject (character) contains the subject codes and the column level (factor) holds the level of the courses (basic and advanced) pupils were tested in. The column result (integer) contains the test results (1 and 2 are positive, 3 and 4 are negative, NA means that the pupil missed the test and 0 means that something else went wrong).

We want to use the following lama-dictionary in order to translate the data frame variables:

Translate using non-standard evaluation

The function lama_translate() uses non-standard evaluation, which means that we pass in expressions, which will be parsed and we can spare the quotes surrounding column and translation names:

The arguments .data and dictionary define which data frame should be translated and which lama-dictionary should be used for the translation. The argument keep_order defines for each given translation if the original ordering of the variable should be kept (ordering of the variable in the data frame df) or if the ordering given in the translation should be used. The argument to_factor defines for each translation, if the resulting labeled variable should be a factor variable (to_factor = TRUE) or a plain character variable (to_factor = FALSE). Besides the arguments .data, dictionary and keep_order all other arguments are label assignments. The names of the arguments (left hand side of the equations) define the column names under which the labeled variable should be stored. The right hand side of the assignments define the column which should be labeled (parameter name in the brackets) and which translation should be used (function name the left of the brackets). Hence, the statement above does the following things:

  • subject_new = sub(subject): The column subject in the data frame df is translated using the translation sub and the resulting factor is stored under the column name subject_new. Since the first entry in keep_order is FALSE, the ordering given in the translation sub is used for the labels. Since the first entry in to_factor is TRUE the resulting variable is a factor variable.
  • level = lev(level): The column level in the data frame df is translated using the translation lev and then overwritten by the resulting factor. Since the second entry in keep_order is TRUE, the labeled variable has the same ordering as the original column. Since the second entry in to_factor is TRUE the resulting variable is a factor variable.
  • result = result(result): The column result in the data frame df is translated using the translation result and then overwritten by the resulting factor. Since the third entry in keep_order is FALSE, the ordering given in the translation is used for the labels. Since the third entry in to_factor is FALSE the resulting variable is a plain character variable.

There are several abbreviations, in order to spare some writing:

  • If the translation has the same name as the original column name, then it is sufficient to just write the translation name on the right hand side. E.g: result_new = result is the same as result_new = result(result).
  • If the column name under which the labeled variable should be stored is the same as the original column name, then the left hand side of the assignment can be omitted. E.g: lev(level) is the same as level = lev(level).
  • If the names of the translation, of the original column and the new column are equal then only the name of the translation is needed. E.g: result is the same as result = result(result).

Translate using standard evaluation

The function lama_translate_() is the standard evaluation variant of lama_translate(), which means that instead of expressions, we pass in character strings holding the names of the translations and columns we want to use:

The arguments .data and dictionary define which data frame should be translated and which lama-dictionary should be used for the translation. The argument keep_order defines for each given translation if the original ordering of the variable should be kept (ordering of the variable in the data frame df) or if the ordering given in the translation should be used. The result is the same as before, when we used lama_translate().

Translate all possible variables

The function lama_translate_all() is an extension of lama_translate(), which tries to automatically translate as many columns in the data frame .data as possible. Therefore, the names of the columns which should be translated must match the names of the translations which should be used:

In the above example, only the column name result matches the translation name and is therefore translated and stored under the column name new_RESULT_labeled. The name of the new columns is a transformation of the old column name (e.g. result), appending the strings given in the arguments prefix and suffix at the beginning and at the end of the column name. Before this string concatenation, the name of the original column can be transformed into a other string by using the string transformation function fn_colname. In our case fn_colname is given the function toupper which transforms all letters of the column name result to upper case RESULT. Contrary to lama_translate(), the argument keep_order is just a single boolean flag. It defines whether the original order of all columns should be kept (keep_order = TRUE) or if the order in the translation vector should be used. Like in the case of lama_translate(), it is possible to pass an argument to_factor = FALSE lama_translate_all in order to define that all resulting labeled variables shall be stored as plain character vectors.

Translate vectors

So far, we only translated variables in data frames, but it is also possible to use lama_translate() and lama_translate_() in order to translate atomic vectors (character, logical, numeric) and factors.

Using lama_translate():

vec <- c("eng", "eng", "gym", "mat")
vec_labeled <- lama_translate(vec, dict, sub)

Using lama_translate_():

Turn labeled variables into factors

Sometimes, you already have labeled variables (character or factor variables, maybe produced by lama_translate() with argument to_factor = FALSE) and you want to turn them into factor variables with a desired ordering. In this case the functions lama_to_factor(), lama_to_factor_() lama_to_factor_all() are right choices.

Let df_non_factor a data frame holding the right labels, but no factor variables (created with lama_translate_all() using to_factor = FALSE):

Turning variables into factors with lama_to_factor():

The function lama_to_factor() allows the same abbreviations as lama_translate(). It can also be used on factor variables and there is also a keep_order argument like in the case of lama_translate(). Furthermore, the functions lama_to_factor() and lama_to_factor_() can both be applied to atomic vectors or plain factors like in the case of lama_translate().

Turning variables in a data frame into factors with lama_to_factor_():

Since the argument col_new was omitted, the variable names (subject, level and result) were overwritten.

Turning all possible variables in a data frame into factors with lama_to_factor_all():

Since the arguments prefix, suffix and fn_colname were omitted, the variable names (subject, level and result) were overwritten.