Create Consecutive Group ID Number in R (Example Code)

This article shows how to create an ID number by group in the R programming language.

Creation of Example Data

data(iris)                                                        # Example data
head(iris)                                                        # Head of example data
#   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa

Example: Creating Group ID Variable

iris_new <- transform(iris, my_id = as.numeric(factor(Species)))  # Adding ID column
head(iris_new)                                                    # Head of data with ID
#   Sepal.Length Sepal.Width Petal.Length Petal.Width Species my_id
# 1          5.1         3.5          1.4         0.2  setosa     1
# 2          4.9         3.0          1.4         0.2  setosa     1
# 3          4.7         3.2          1.3         0.2  setosa     1
# 4          4.6         3.1          1.5         0.2  setosa     1
# 5          5.0         3.6          1.4         0.2  setosa     1
# 6          5.4         3.9          1.7         0.4  setosa     1

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