A character vector of variables to join by. This variables is
passed to the by term in a dplyr::left_join() and inherits its
behavior:
If NULL, the default, the join will perform a natural join, using all
variables in common across the parameters and
additional_data.
To join by different variables on parameters and
additional_data, use a named vector. For example,
by = c("k" = "cluster_size") will match parameters$k to
additional_data$cluster_size.
To join by multiple variables, use a vector with length > 1. For example,
by = c("k", "summation_method") will match parameters$k to
additional_data$k and parameters$summation_method to
additional_data$summation_method. Use a named vector to match different
variables in parameters and additional_data.
For example, by = c("k" = "cluster_size", "summation_method" = "sm")
will match parameters$k to additional_data$cluster_size and
parameters$summation_method to additional_data$sm.