How to Calculate Percentage by Group in R

In R Programming Language Percentage by group refers to calculating the proportion or percentage of a certain subgroup within a larger group. This is often used in statistics or data analysis to understand the distribution of data across different categories or groups.

Calculation of the percentage by group

• Identify the groups: Determine the categories or subgroups within the dataset that are needed to analyze.
• Count the occurrences: Count the number of occurrences or instances within each group.
• Calculate the total: Find the total number of occurrences in the entire dataset.
• Calculate the percentage: Divide the count of each subgroup by the total count and multiply by 100 to get the percentage.

Percentage by Group = (Count of subgroup/Total count)*100%

For example, you have a dataset of students’ grades categorized by gender

• Total number of students: 100
• Number of male students: 40
• Number of female students: 60

To calculate the percentage of male and female students

• Percentage of male students: (40/100)*100%=40%
• Percentage of female students: (60/100)*100%=60%

This shows that 40% of the students are male, and 60% are female. This method helps in understanding the distribution of data and identifying any patterns or trends within different groups.

In R, “Percentage by Group” typically refers to calculating the percentage of a variable within each group defined by another variable. Calculating percentages by group in R can be done using various packages like dplyr or data.table.

Calculate Percentage by Group in R using ‘dplyr’ package

R

# Load the dplyr package
library(dplyr)

# Example data
data <- data.frame(
  group = c("A", "A", "B", "B", "B", "C", "C", "C"),
  value = c(10, 20, 15, 25, 30, 12, 18, 20)
)

# Group by 'group' and calculate the percentage within each group
result <- data %>%
  group_by(group) %>%
  mutate(percentage = value / sum(value) * 100)

# View the result
print(result)

Output:

A tibble: 8 × 3
# Groups:   group [3]
  group value percentage
  <chr> <dbl>      <dbl>
1 A        10       33.3
2 A        20       66.7
3 B        15       21.4
4 B        25       35.7
5 B        30       42.9
6 C        12       24  
7 C        18       36  
8 C        20       40  

Calculate Percentage by Group using ‘data.table’ package

R

# Load the data.table package
library(data.table)

# Convert data to data.table
data <- data.table(
  group = c("X", "Y", "Z", "Z", "Z", "M", "M", "M"),
  value = c(16, 20, 15, 25, 40, 14, 18, 30)
)

# Calculate percentage by group
result <- data[, percentage := value / sum(value) * 100, by = group]

# View the result
print(result)

Output:

   group value percentage
1:     X    16  100.00000
2:     Y    20  100.00000
3:     Z    15   18.75000
4:     Z    25   31.25000
5:     Z    40   50.00000
6:     M    14   22.58065
7:     M    18   29.03226
8:     M    30   48.38710

Now we Calculate percentages by species for iris dataset

R

# Load the required packages
library(dplyr)

# Calculate the percentage of each species
species_percentages <- iris %>%
  group_by(Species) %>%
  summarise(percentage = n() / nrow(iris) * 100)

# Print the result
print(species_percentages)

Output:

# A tibble: 3 × 2
  Species         percentage
  <chr>                <dbl>
1 Iris-setosa           33.3
2 Iris-versicolor       33.3
3 Iris-virginica        33.3

In this scenario, we calculate the percentage of each species (setosa, versicolor, virginica) in the iris dataset. We use ‘dplyr’ to group the data by the ‘Species’ column and then calculate the count of each species divided by the total number of observations in the dataset to obtain the percentage.

Calculate percentages by species and petal length category

R

# Load the required packages
library(dplyr)
# Create categories for petal length
iris <- iris %>%
  mutate(petal_length_category = cut(Petal.Length, breaks = c(0, 2, 4, 6, Inf), 
                                   labels = c("Short", "Medium", "Long", "Extra Long")))

# Calculate the percentage of each species within each petal length category
species_percentages <- iris %>%
  group_by(Species, petal_length_category) %>%
  summarise(percentage = n() / nrow(iris) * 100)

# Print the result
print(species_percentages)

Output:

# A tibble: 5 × 3
# Groups:   Species [3]
  Species    petal_length_category percentage
  <fct>      <fct>                      <dbl>
1 setosa     Short                       33.3
2 versicolor Medium                      10.7
3 versicolor Long                        22.7
4 virginica  Long                        27.3
5 virginica  Extra Long                   6  

Here, we create categories for petal length (short, medium, long, extra long) and calculate the percentage of each species within each petal length category. We use ‘dplyr’ to group the data by both ‘Species’ and ‘petal_length_category’ columns and then calculate the count of each species within each category divided by the total number of observations to obtain the percentage.

Conclusion

In summary, calculating “Percentage by Group” in R enables us to understand how a variable is distributed across different subgroups or categories. Utilizing tools like dplyr, we can efficiently analyze relative proportions within each group, revealing insights into patterns, trends, or disparities.