Reads the specified variables from the SQLite database.
read_variables(path, variables, freq, prep_fun, aggr_funs, postp_funs)A list of variables read from the database.
[mandatory] (character) Path to the root directory of the generated database.
[mandatory] (character) A vector of variable names to read.
[mandatory] (character or NULL) Specifies the frequency
to aggregate the data. If NULL, no aggregation is performed and
native dates are returned.
[mandatory] (function) Pre-processing function applied
after daily expansion and before aggregation (used only when
freq is not NULL). Passing NULL is handled in
read_db(), so this argument is always a function here.
[optional] (function or list) Aggregation function(s) used
when aggregating to freq.
If a single function is provided, it is used for all variables.
If an unnamed list of functions is provided, all functions are
applied to all variables (treated as default).
If a named list is provided, names must be variable names (as
returned by fetch_vars) and/or "default"; named entries
override the default for those variables.
[optional] (function or list or "external") Post-
processing function(s) applied after aggregation.
If a single function or NULL is provided, it is used for
all variables as default.
If an unnamed list of functions is provided, all are applied to
all variables (treated as default).
If a named list is provided, names must be variable names (as
returned by fetch_vars) and/or "default"; named entries
override the default for those variables.
If "external", functions are loaded from postp/.
Default is NULL.