Arrange() does not work within for loop in R - for-loop

Question

Nice to meet you all. This is my first question in this wonderful place. Thank you in advance for your time and problem-solving efforts.
I want to see the top 10 donor countries' names each year.
My data looks like this.
head(Afghanistan)
# A tibble: 6 × 62
Donor Y_1960 Y_1961 Y_1962 Y_1963 Y_1964 Y_1965 Y_1966 Y_1967 Y_1968 Y_1969 Y_1970 Y_1971 Y_1972 Y_1973 Y_1974 Y_1975 Y_1976 Y_1977 Y_1978
<chr> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
1 Austral… NA NA NA NA NA 0.03 0.04 0.04 0.06 0.74 0.1 0.12 0.15 0.58 0.15 0.25 0.26 0.65 1.03
2 Austria NA NA NA NA 0.02 0.02 0.03 0.05 0.02 0.01 NA 0.05 NA NA NA NA 0.03 0.09 0.08
3 Belgium NA NA NA NA NA NA NA NA NA NA NA NA NA 0.01 0.01 0.01 0.04 0.03 0.06
4 Canada NA NA NA NA NA 0.01 0.03 0.03 0.01 0.01 0.7 2.14 1.14 2.22 0.54 1.47 0.38 0.34 4.19
5 Czech R… NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
6 Denmark NA NA NA NA NA NA NA 0.01 0.02 0.02 0.02 0.02 0.05 0.12 0.05 0.93 2.57 0.06 0.41
# … with 42 more variables
head(DAC)
iso2c country year unemp unemp_ILO gdpgrowth gdppc iso3c
6 AT Austria 1965 NA NA 3.480175 2.810013 AUT
7 AT Austria 1966 NA NA 5.642861 4.904479 AUT
8 AT Austria 1967 NA NA 3.008048 2.241010 AUT
9 AT Austria 1968 NA NA 4.472313 3.931242 AUT
10 AT Austria 1969 2.8 NA 6.275867 5.909496 AUT
11 AT Austria 1970 2.4 NA 6.321143 5.950497 AUT
Before making a for loop, I tried this to test the code.
new <- Afghanistan %>%
select(Donor, Y_1990) %>%
arrange(desc(Y_1990)) %>%
drop_na() %>%
slice_max(Y_1990, n=10)
new
# A tibble: 10 × 2
Donor Y_1990
<chr> <dbl>
1 United States 56
2 Sweden 16.0
3 Germany 8.07
4 Norway 3.35
5 Netherlands 3.13
6 Canada 2.73
7 United Kingdom 2.39
8 Switzerland 2.01
9 France 1.87
10 Denmark 1.58
When I run the above code, arrange() works well. However, after using it within for loop, it only shows alphabetical order by country names.
year <- seq(1960, 2020, 1)
for(i in year){
Year <- paste0("Y", "_", i)
new <- Afghanistan %>%
select(Donor, Year) %>%
arrange(desc(Year)) %>%
drop_na()
print(new[1:10, 1])
}
# A tibble: 10 × 2
Donor Y_1990
<chr> <dbl>
1 Australia 1.23
2 Austria 1.49
3 Belgium 0.01
4 Canada 2.73
5 Denmark 1.58
6 Finland 0.15
7 France 1.87
8 Germany 8.07
9 Ireland 0.05
10 Japan 0.03
# A tibble: 10 × 2
Donor Y_1991
<chr> <dbl>
1 Australia 4.75
2 Austria 0.62
3 Canada 5.31
4 Denmark 2.71
5 Finland 2.28
6 France 1.5
7 Germany 5.52
8 Italy 0.4
9 Japan 0.02
10 Korea 0.11
Like the above, the results are not arranged by the value of Year. How should I fix this? I tried to use rank() but it also only gives alphabetical results.

Answer 1

You have fallen victim to the intricacies of non-standard evaluation. You need to quote-unquote Year like this:
arrange(!!sym(Year))
In this case when you use arrange it is expecting a column named Year so you have to do something special that tells arrange to use the value assigned to Year.
Not you might be asking: "why doesn't select have this problem?" And the answer is it does behave this way but it also tries to figure out what you meant if you don't "quote-unquote" In fact you should see a warning the first time you do this in your session. In this case the solution is to do something like this:
select(all_of(Year))
Some reading on NSE:
https://www.r-bloggers.com/2019/07/bang-bang-how-to-program-with-dplyr/
https://www.brodrigues.co/blog/2019-06-20-tidy_eval_saga/
http://adv-r.had.co.nz/Computing-on-the-language.html
And some other SO posts on this matter:
How do {{}} double curly brackets work in dplyr?
Turn a {{}} (dplyr double curly braces) interpolation into a string