How to assign unique country ID number in panel data frame in R - r

Question

In my dataset, I want to create unique country id numbers. Any help?
library(dplyr)
library(pwt10)
dataframe looks like
country isocode year currency gdp inflation ...
Aruba ABW 1950 N/A N/A N/A
Aruba ABW 1950 N/A N/A N/A
Aruba ABW 1950 N/A N/A N/A
Aruba ABW 1950 N/A N/A N/A
...
Argentina ARG 1950 Peso 130 60 ...
I want to create another column of country ID variable (id_num), whose values are written in descending order (1,2,3,....) so that it looks like the following:
country isocode year currency gdp inflation ID
Aruba ABW 1950 N/A N/A N/A 1
Aruba ABW 1950 N/A N/A N/A 1
Aruba ABW 1950 N/A N/A N/A 1
Aruba ABW 1950 N/A N/A N/A 1
...
Argentina ARG 1950 Peso 130 60 ... 5
`
I was wondering how to create the unique country ID column. Any help?

Answer 1

If I understood your task correctly you are looking to build a second (first is the isocode) group identification by sequencial numbering of groups. One way to achive this is the cur_group_id() function from dplyr. Here is a toy example you should be able to adapt to your data.frame:
library(dplyr)
# dummy data
df <- data.frame(col1 = c("a", "a", "b", "b", "b", "c") ,
col2 = 1:6)
df %>%
# arrange the data in growing order for column you want to build sequential group ID from/for
dplyr::arrange(col1) %>%
# build the groupings
dplyr::group_by(col1) %>%
# add new column : sequenctial group id
dplyr::mutate(ID = dplyr::cur_group_id()) %>%
# always ungroup to prevent unwanted behaviour down stream
dplyr::ungroup()
# A tibble: 6 x 3
col1 col2 ID
<chr> <int> <int>
1 a 1 1
2 a 2 1
3 b 3 2
4 b 4 2
5 b 5 2
6 c 6 3

Answer 2

Do you mean that "ARM" should return 1, "AUS" should return 2 and so on.
Maybe you can try this answer with match.
library(dplyr)
result <- pwt10.0 %>%
filter(isocode %in% comparison_states) %>%
distinct(isocode) %>%
mutate(id_num = match(comparison_states, isocode))
result
# isocode id_num
#ARM-1950 ARM 1
#AUS-1950 AUS 2
#CAN-1950 CAN 3
#CHN-1950 CHN 4
#GBR-1950 GBR 5
#ITA-1950 ITA 6
#JPN-1950 JPN 7
#LUX-1950 LUX 8
#NOR-1950 NOR 9
#NZL-1950 NZL 10
#SGP-1950 SGP 11
#SWE-1950 SWE 12
#THA-1950 THA 13
#TWN-1950 TWN 14
#USA-1950 USA 15