The split() function in R is used to split a data frame or other R object according to the levels of a variable or variables. This can be useful for a variety of tasks, such as summarizing data by group, performing statistical tests on different groups, or plotting data by group.
The basic syntax for the split() function is:
split(object, factors, drop = FALSE)
- `object` is the R object to be split. This can be a data frame, a vector, a list, or any other R object that can be indexed by a factor.
- `factors` is a vector of factors that define the levels to split the object by.
- `drop` is a logical value that determines whether to drop empty levels from the resulting split object.
For example, the following code splits the airquality data frame by the Month variable:
s <- split(airquality, airquality$Month)
This results in a list of 5 data frames, one for each month. The data frames in the list can be accessed by their names, which are the levels of the Month variable. For example, to access the data frame for May, we would use the following code:
s$May
The split() function can also be used to split an object according to the levels of multiple variables. For example, the following code splits the airquality data frame by the Month and Day variables:
s <- split(airquality, list(airquality$Month, airquality$Day))
This results in a list of 60 data frames, one for each combination of month and day. The data frames in the list can be accessed by their names, which are the combinations of the levels of the Month and Day variables. For example, to access the data frame for May 1st, we would use the following code:
s$`5-1`
