You can use the **dcast** function from the **data.table** package in R to reshape a data frame from a long format to a wide format.

This function is particularly useful when you want to summarize specific variables in a data frame, grouped by other variables.

The following examples show how to use the **dcast** function in practice with the following data frame in R:

library(data.table) #create data frame df <- data.frame(team=c('A', 'A', 'A', 'A', 'B', 'B', 'B', 'B'), position=c('G', 'G', 'F', 'F', 'G', 'G', 'F', 'F'), points=c(18, 13, 10, 12, 16, 25, 24, 31), assists=c(9, 8, 8, 5, 12, 15, 10, 7)) #convert data frame to data table dt <- setDT(df) #view data table dt team position points assists 1: A G 18 9 2: A G 13 8 3: A F 10 8 4: A F 12 5 5: B G 16 12 6: B G 25 15 7: B F 24 10 8: B F 31 7

**Example 1: Calculate Metric for One Variable, Grouped by Other Variables**

The following code shows how to use the **dcast** function to calculate the mean **points** value, grouped by the **team** and **position** variables:

library(data.table) #calculate mean points value by team and position dt_new <- dcast(dt, team + position ~ ., fun.aggregate = mean, value.var = 'points') #view results dt_new team position . 1: A F 11.0 2: A G 15.5 3: B F 27.5 4: B G 20.5

**Example 2: ****Calculate Multiple Metrics for One Variable, Grouped by Other Variables**

The following code shows how to use the **dcast** function to calculate the mean **points** value and the max **points** value, grouped by the **team** and **position** variables:

library(data.table) #calculate mean and max points values by team and position dt_new <- dcast(dt, team + position ~ ., fun.aggregate = list(mean, max), value.var = 'points') #view results dt_new team position points_mean points_max 1: A F 11.0 12 2: A G 15.5 18 3: B F 27.5 31 4: B G 20.5 25

**Example 3: ****Calculate Metric for Multiple Variables, Grouped by Other Variables**

The following code shows how to use the **dcast** function to calculate the mean **points** value and mean **assists** value, grouped by the **team** and **position** variables:

library(data.table) #calculate mean and max points values by team and position dt_new <- dcast(dt, team + position ~ ., fun.aggregate = mean, value.var = c('points', 'assists')) #view results dt_new team position points assists 1: A F 11.0 6.5 2: A G 15.5 8.5 3: B F 27.5 8.5 4: B G 20.5 13.5

**Additional Resources**

The following tutorials provide additional information about data tables:

data.table vs. data frame in R: Three Key Differences

How to Filter a data.table in R

How to Use rbindlist in R to Make One Data Table from Many