foreach with variables and packages

The rate at which a population grows is called the growth rate, expressed as a percentage. Almost every country is experiencing a drop in growth rate, but some are declining faster than others.

You were hired as a Demographics Analyst, and your task is to calculate the the ratio between a country's population growth rate and the global growth rate for the years 2017 to 2021. You have been given a list of data frames, ls_df, each is a data frame like this:

    country year growth_rate
Afghanistan 2017        2.52
...

You also have a global growth data frame, df_global:

year global_growth
2017          1.15
...

foreach and dplyr have been loaded for you. The cluster has already been created and registered with the foreach backend.

This exercise is part of the course

Parallel Programming in R

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Exercise instructions

Export df_global to the cluster within the foreach() function call.
Specify the dplyr package required for the calculation.
Specify rbind as the combine method.
Use the parallel operator.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

df_comp <- foreach(df = ls_df,
                   # Export variable
                   ___,
                   # Specify any package needed
                   ___,
                   # Specify a combine method 
                   ___
                   # Use the parallel operator
                  ) ___ {
    df %>%
      left_join(df_global, "year") %>% 
      mutate(comp = growth_rate/global_growth)
}

stopCluster(cl)

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