You can use the following basic syntax to calculate the correlation between two variables by group in R:

library(dplyr) df %>% group_by(group_var) %>% summarize(cor=cor(var1, var2))

This particular syntax calculates the correlation between **var1** and **var2**, grouped by **group_var**.

The following example shows how to use this syntax in practice.

**Example: Calculate Correlation By Group in R**

Suppose we have the following data frame that contains information about basketball players on various teams:

**#create data frame
df <- data.frame(team=c('A', 'A', 'A', 'A', 'B', 'B', 'B', 'B'),
points=c(18, 22, 19, 14, 14, 11, 20, 28),
assists=c(2, 7, 9, 3, 12, 10, 14, 21))
#view data frame
df
team points assists
1 A 18 2
2 A 22 7
3 A 19 9
4 A 14 3
5 B 14 12
6 B 11 10
7 B 20 14
8 B 28 21
**

We can use the following syntax from the dplyr package to calculate the correlation between **points** and **assists**, grouped by **team**:

library(dplyr) df %>% group_by(team) %>% summarize(cor=cor(points, assists)) # A tibble: 2 x 2 team cor 1 A 0.603 2 B 0.982

From the output we can see:

- The correlation coefficient between points and assists for team A is
**.603**. - The correlation coefficient between points and assists for team B is
**.982**.

Since both correlation coefficients are positive, this tells us that the relationship between points and assists for both teams is positive.

**Related:** What is Considered to Be a “Strong” Correlation?

**Additional Resources**

The following tutorials explain how to perform other common operations in R:

How to Count Unique Values by Group in R

How to Calculate the Sum by Group in R

How to Calculate the Mean by Group in R

How to Calculate Summary Statistics by Group in R

Thanks. One glance at your tutorial and I get what I need — as usual. Thanks for making things so clear with great examples!