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