Mr.ecos Mr.ecos -4 years ago 251
R Question

Assign unique ID to distinct values within Group with dplyr

Problem: I need to make a unique ID field for data that has two levels of grouping. In the example code here, it is

Emp
and
Color
. The ID needs to be structured as:

Emp
+ unique number of each
Color
+ sequential number for duplicated
Colors
.

These values are separated by periods.

Example data:

dat <- data.frame(Emp = c("A","A","A","B","B","C"),
Color = c("Red","Green","Green","Orange","Yellow","Brown"),
stringsAsFactors = FALSE)


The ID is supposed to appear as this:

ID <- c("A.01.001", "A.02.001", "A.02.002", "B.01.001", "B.02.001", "C.01.001")



ID
[1] "A.01.001" "A.02.001" "A.02.002" "B.01.001" "B.02.001" "C.01.001"


The three character suffix to the ID to record the duplicates can be done as:

group_by(dat, Emp, Color) %>%
mutate(suffix = str_pad(row_number(), width=3, side="left", pad="0"))


But I am unable to assign sequential numbers to the unique occurrence of
Color
with each
Emp
group.

I prefer a dplyr solution, but any method would be appreciated.

Answer Source

Using data.table and sprintf:

library(data.table)
setDT(dat)[, ID := sprintf('%s.%02d.%03d', 
                           Emp, rleid(Color), rowid(rleid(Color))), 
           by = Emp]

you get:

> dat
   Emp  Color       ID
1:   A    Red A.01.001
2:   A  Green A.02.001
3:   A  Green A.02.002
4:   B Orange B.01.001
5:   B Yellow B.02.001
6:   C  Brown C.01.001

How this works:

  • You convert dat to a data.table with setDT()
  • Group by Emp.
  • And create the ID-variable with the sprintf-function. With sprintf you paste several vector easily together according to a specified format.
  • The use of := means that the data.table is updated by reference.
  • %s indicates that a string is to be used in the first part (which is Emp). %02d & %03d indicates that a number needs to have two or three digits with a leading zero(s) when needed. The dots in between will taken literally and thus in cluded in the resulting string.

Adressing the comment of @jsta, if the values in the Color-column are not sequential you can use:

setDT(dat)[, r := as.integer(factor(Color, levels = unique(Color))), by = Emp
           ][, ID := sprintf('%s.%02d.%03d', 
                             Emp, r, rowid(r)), 
             by = Emp][, r:= NULL]

This will also maintain the order in which the Color column is presented. Instead of as.integer(factor(Color, levels = unique(Color))) you can also use match(Color, unique(Color)) as shown by akrun.

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