Author(s) John Fox jfox@mcmaster.ca. For instance, measure the average or group … tapply in R Apply a function to each cell of a ragged array, that is to each (non-empty) group of values given by a unique combination of the levels of certain factors. Aggregate Group-Bys. .data: A data frame, data frame extension (e.g. Applies a function, typically to compute a single statistic, like a mean, median, or standard deviation, within levels of a factor or within combinations of levels of two or more factors to produce a table of statistics. I have a data frame like the following: a b1 b2 b3 b4 b5 b6 b7 b8 b9 D 4 6 9 5 3 9 7 9 8 F 7 3 8 1 3 1 4 4 3 R 2 5 5 1 4 2 3 1 6 D ... That's because tapply works on vectors, and transforms df[,2:10] to a vector. tapply(X, INDEX, FUN = NULL) Arguments: -X: An object, usually a vector -INDEX: A list containing factor -FUN: Function applied to each element of x. The function given by fun is applied to the values of the left-hand-side variable in formula within (combination of) levels of the factor(s) given in the right-hand side of formula, producing a table of statistics.. Value. Related. In this article we have seen common methodologies to perform group manipulation in R. Extract a dplyr tbl column as a vector. 791. data.table vs dplyr: can one do something well the other can't or does poorly? a tibble), or a lazy data frame (e.g. Group by one or more variables. The object returned by tapply, typically simply printed.. View all posts by Zach Post navigation. In this tutorial, you will learn In the case below for both tapply and by you have some a factor variable cyl for which you want to execute a function mean over the corresponding cases in vector of numbers mpg. R has built-in apply function and all of its relatives such as tapply, lapply, sapply and mapply. Part of the job of a data scientist or researchers is to compute summaries of variables. This function provides a formula interface to the standard R -10" data-mini-rdoc="car::tapply">tapply function.