# Calculate Sum by Group & Assign as New Variable to Data Frame in R (Example Code)

This article explains how to get the mean by group and assign the output as a new variable to a data frame in R.

## Creation of Example Data

```data(iris) # Loading example data head(iris) # 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: Append Sum by Group as a New Variable to a Data Frame Using the dplyr Package

```install.packages("dplyr") # Install dplyr package library("dplyr") # Load dplyr```
```iris_new <- iris %>% # Computing mean by group group_by(Species) %>% mutate(SL_sum = sum(Sepal.Length)) head(iris_new) # # A tibble: 6 × 6 # # Groups: Species [1] # Sepal.Length Sepal.Width Petal.Length Petal.Width Species SL_sum # <dbl> <dbl> <dbl> <dbl> <fct> <dbl> # 1 5.1 3.5 1.4 0.2 setosa 876. # 2 4.9 3 1.4 0.2 setosa 876. # 3 4.7 3.2 1.3 0.2 setosa 876. # 4 4.6 3.1 1.5 0.2 setosa 876. # 5 5 3.6 1.4 0.2 setosa 876. # 6 5.4 3.9 1.7 0.4 setosa 876.```

## Related Articles

Have a look at the following R tutorials. They discuss topics such as dplyr, vectors, loops, and missing data.