Most efficient way to gsub strings in awk where strings come from a separate file - awk

Question

I have a tab-sebarated file called cities that looks like this:
Washington Washington N 3322 +Geo+Cap+US
Munich München N 3842 +Geo+DE
Paris Paris N 4948 +Geo+Cap+FR
I have a text file called countries.txt which looks like this:
US
DE
IT
I'm reading this file into a Bash variable and sending it to an awk program like this:
#!/usr/bin/env bash
countrylist=$(<countries.txt)
awk -v countrylist="$countrylist" -f countries.awk cities
And I have an awk file which should split the countrylist variable into an array, then process the cities file in such a way that we replace "+"VALUE with "" in $5 only if VALUE is in the countries array.
{
FS = "\t"; OFS = "\t";
split(countrylist, countries, /\n/)
# now gsub efficiently every country in $5
# but only if it's in the array
# i.e. replace "+US" with "" but not
# "+FR"
}
I am stuck in this last bit because I don't know how to check if $5 has a value from the array countries and to remove it only then.
Many thanks in advance!
[Edit]
The output should be tab-delimited:
Washington Washington N 3322 +Geo+Cap
Munich München N 3842 +Geo
Paris Paris N 4948 +Geo+Cap+FR

Answer 1

Could you please try following, if I understood your requirement correctly.
awk 'FNR==NR{a[$0]=$0;next} {for(i in a){if(index($5,a[i])){gsub(a[i],"",$5)}}} 1' countries.txt cities
A non-one liner form of code is as follows(you could set FS and OFS to \t in case your Input_file is TAB delimited):
awk '
FNR==NR{
a[$0]=$0
next
}
{
for(i in a){
if(index($5,a[i])){
gsub(a[i],"",$5)
}
}
}
1
' countries.txt cities
Output will be as follows.
Washington Washington N 3322 +Geo+Cap+
Munich München N 3842 +Geo+
Paris Paris N 4948 +Geo+Cap+FR

Answer 2

This is the awk way of doing it:
$ awk '
BEGIN {
FS=OFS="\t" # delimiters
}
NR==FNR { # process countries file
countries[$0] # hash the countries to an array
next # skip to next citi while there are cities left
}
{
n=split($5,city,"+") # split the 5th colby +
if(city[n] in countries) # search the last part in countries
sub(city[n] "$","",$5) # if found, replace in the 5th
}1' countries cities # output and mind the order of files
Output (with actual tabs in data):
Washington Washington N 3322 +Geo+Cap+
Munich München N 3842 +Geo+
Paris Paris N 4948 +Geo+Cap+FR