Replacing items in a list with items from another list in R - r

Question

I have a column in a list with country codes in characters, I want to replace these with numeric codes. for the "decoding" I have a second list where the character country codes are associated with the numeric codes.
I tried gsub:
for (i in 1:nrow(countries))
{gsub(countries$code3[i], countries$numcode[i], doc_report$nationality)}
I tried a for loop:
i <- NULL
n <- NULL
for (i in 1:nrow(doc_report)) {
for (n in 1:nrow(countries)) {
if(doc_report$nationality[i] == countries$code3[n])
doc_report$nationality[i] <- countries$numcode[n]
else
if(doc_report$nationality[i] == "NA")
doc_report$nationality[i] <- 000
}
}
and I had something in mind with merge()
this is how the column looks like that has to be replaced
[nationality] IRL GBR ITA FRA POL BRA ESP GBR GBR GBR
this is how the second table for decoding looks like:
[code3] AFG ALB DZA ASM AGO AIA ATG ARG ARM
[numcode] 4 8 12 16 24 660 NA 28 32 51
so in table one I want the numcode from table 2 rather than the code3 style.

Answer 1

Updated Answer
Here's an example with data formatted like yours to make it clearer that it does work despite duplicate country codes.
library(tidyverse)
country <- c("IRL", "GBR", "ITA", "FRA", "POL", "BRA", "ESP")
codes <- c(1,2,3,4,5,6,7)
countries <- tibble(country, codes)
doc_report <- tibble(x=c("a","b","c","d","e"),
country = c("ITA","ITA", "POL", "BRA","ESP"))
left_join(doc_report, countries, by="country")
The output of this code is:
# A tibble: 5 x 3
x country codes
<chr> <chr> <dbl>
1 a ITA 3
2 b ITA 3
3 c POL 5
4 d BRA 6
5 e ESP 7
Which I believe is the behavior you're looking for.
Original Answer
A simple solution would be to use the left_join() function in the dplyr package and then select() to remove the unneeded column.
Let's say doc_report keys countries by code and country_codes is a tibble with 1 column of country string codes and 1 column of corresponding numerical codes, you could do something like this
## join the country codes
doc_report <- left_join(doc_report, country_codes, by="code3")
## remove the unneeded column
doc_report <- select(doc_report, -code3)
Does this make sense? Happy to expand otherwise.