R : Generate a sequential column based on data from another column

Question

I have a dataframe 'my_data' which looks like this:

Calendar_Day      Name    
2018-03-31        ABC    
2018-03-31        XYZ  
2018-03-31        OPR
2019-01-31        ABC    
2019-01-31        RTE    
2019-10-31        YUD    
2018-03-31        RYT

I wish to have another column that will serve as a primary key with a format

YEAR+MONTH+6digit sequence  , eg: 201803000001

I am new to R and couldn't find a way to implement the concept.

and Dataframe should look like

Calendar_Day      Name    ID
2018-03-31        ABC     201803000001
2018-03-31        XYZ     201803000002
2018-03-31        OPR     201803000003
2019-01-31        ABC     201901000001
2019-01-31        RTE     201901000002
2019-10-31        YUD     201910000001
2018-03-31        RYT     201803000004

Answer 1

library(dplyr)
library(lubridate)
d %>%
    mutate(Date = ymd(Date)) %>%
    group_by(tmp1 = year(Date), tmp2 = month(Date)) %>%
    mutate(ID = paste0(year(Date),
                       sprintf("%02d", month(Date)),
                       sprintf("%05d", row_number()))) %>%
    ungroup() %>%
    select(-tmp1, -tmp2)
#> # A tibble: 7 x 3
#>   Date       Name  ID         
#>   <date>     <chr> <chr>      
#> 1 2018-03-31 ABC   20180300001
#> 2 2018-03-31 XYZ   20180300002
#> 3 2018-03-31 OPR   20180300003
#> 4 2019-01-31 ABC   20190100001
#> 5 2019-01-31 RTE   20190100002
#> 6 2019-10-31 YUD   20191000001
#> 7 2018-03-31 RYT   20180300004

Answer 2

you could use the tidyverse package like this:

library(tidyverse)

mydata  %>%
  mutate(Date2 = format(Date, "%Y%m")) %>%
  group_by(Date2) %>%
  mutate(ID = paste0(Date2, str_pad(1:n(), width = 6, side = "left",  pad = "0"))) %>%
  ungroup() %>%
  select(-Date2)

The main idea is to use the format function: format(mydate, %Y) returns the year of a date object and format(mydate, %m) returns the month of a date object. I paste these two together and add the six digit sequence. I use string_pad to add leading zeros to the sequence.