R For Dummies by Joris Meys

Author:Joris Meys
Language: eng
Format: epub
Publisher: Wiley
Published: 2012-06-01T04:00:00+00:00

VAT <- sapply(client, switch, private=1.12, public=1.06, 1)

tot.price <- net.price * VAT

round(tot.price)

}

Applying a function to a data frame

You also can use sapply() on lists and data frames. In this case, sapply() applies the specified function on every element in that list. Because data frames are lists as well, everything in this section applies to both lists and data frames.

Imagine that you want to know which type of variables you have in your data frame clients. For a vector, you can use the class() function to find out the type. In order to know this for all variables of the data frame at once, you simply apply the class() function to every variable by using sapply() like this:

> sapply(clients,class)

hours public type

“numeric” “logical” “character”

R returns a named vector that gives you the types of every variable, and it uses the names of the variables as names for the vector. In case you use a named list, R uses the names of the list elements as names for the vector.

Simplifying results (or not) with sapply

The sapply() function doesn’t always return a vector. In fact, the standard output of sapply is a list, but that list gets simplified to either a matrix or a vector if possible.

If the result of the applied function on every element of the list or vector is a single number, sapply() simplifies the result to a vector.

If the result of the applied function on every element of the list or vector is a vector with exactly the same length, sapply() simplifies the result to a matrix.

In all other cases, sapply() returns a (named) list with the results.

Say you want to know the unique values of every variable in the data frame clients. To get all unique values in a vector, you use the unique() function. You can get the result you want by applying that function to the data frame clients like this:

> sapply(clients, unique)

$hours

[1] 25 110 125 40

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