tapply() is a function in R that is used to apply a function over subsets of a vector. It can be thought of as a combination of split() and sapply() for vectors only.
The arguments to tapply() are as follows:
- X is a vector
- INDEX is a factor or a list of factors (or else they are coerced to factors)
- FUN is a function to be applied
- … contains other arguments to be passed FUN
- simplify, should we simplify the result?
For example, let's say we have a vector of numbers and we want to calculate the mean of each group of numbers. We can use tapply() to do this as follows:
x <- c(rnorm(10), runif(10), rnorm(10, 1))
f <- gl(3, 10)
tapply(x, f, mean)
This will return a vector of means, one for each group of numbers.
We can also use tapply() to apply functions that return more than a single value. For example, we can use it to find the range of each group of numbers as follows:
tapply(x, f, range)
This will return a list, one for each group of numbers. Each list will contain the minimum and maximum values of the group.
tapply() is a very versatile function that can be used to apply a variety of functions over subsets of a vector. It is a powerful tool that can be used to summarize data and identify patterns.
