Finding maximum value per row and normalizing to this value

Question

Is there a way to normalize many rows of a data frame according to the maximum value per row, preferably in dplyr?

In iris I want to find the maximum per row of the columns Sepal.length, Sepal.width, Petal.length and Petal.width. I then want to divide every value by this maximum to get a range from 0 to 1. I want to be able to give a range of columns across which to find the maximum, and preferably not have to call them by name.

Output goal:

> iris
Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
5.1          3.5         1.4          0.2            setosa

> iris.normalized
Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
1            3.5/5.1     1.4/5.1      0.2/5.1        setosa

I tried using the max function to no avail. I'm glad for any help.

Answer 1

使用base R ，用pmax计算每行的最大值，然后除以感兴趣的列以进行缩放

iris[1:4] <-  iris[1:4]/do.call(pmax, iris[1:4])