R : fill a column depending on a value and a vector

Question

I have a data frame users with a column id and country

id                  country
1                   France
2                   United States
3                   France

I want to add a new column salary which depends on the average salary for a given country .

My first thought was to create a config vector with (country, salary) like this :

salary_country <- c(
   "France"=45000,
   "United States"=50000,
   ...)

And then to create the column like this (using dplyr ) :

tbl_df(users) %>% 
  mutate(salary = ifelse(country %in% names(salary_country), 
                         salary_country[country], 
                         0))

It runs like a charm. If the country does not exist in my salary_country vector, the salary is equal to 0 else it's equal to the given salary .

But, it is quite slow on a very large data frame and quite verbose.

Is there a better way to accomplish that ?

Answer 1

You can use match :

salary_country[match(users$country, names(salary_country))]

Or go for data.table :

dt = data.table(salary=salary_country, country=names(salary_country))

dt[setDT(users), on='country']

#   salary       country id
#1:  45000        France  1
#2:  50000 United States  2
#3:  45000        France  3