P146 example from the book "R in action" -

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from book "r in action" page 146 has example of group descriptive statistics by

vars <- c("mpg", "hp", "wt") ... > dstats <- function(x)(c(mean=mean(x), sd=sd(x))) > by(mtcars[vars], mtcars$am, dstats)

but when input r 

> error in is.data.frame(x) :  >(list) object cannot coerced type 'double' >in addition: warning message: >in mean.default(x) : argument not numeric or logical: returning na

i not know happens here. can gives me help. thanks.

please ?by() in r console.

in help, you'll find following mentioned fun

by(data, indices, fun, ..., simplify = true)  fun function applied (usually data-frame) subsets of data.

update

this more has way mean() , sd() defined. both on support vector, not data frames.

checkout examples below, , see difference comes mean() , without vectorize(): 

x <- data.frame( = c(1, 2, 4), b = c(1, 2, 4))

now, if do:

by(x, 1:3, mean)

you following error:

warning messages: 1: in mean.default(data[x, , drop = false], ...) :   argument not numeric or logical: returning na 2: in mean.default(data[x, , drop = false], ...) :   argument not numeric or logical: returning na 3: in mean.default(data[x, , drop = false], ...) :   argument not numeric or logical: returning na

but upon adding vectorize():

by(x, 1:3, vectorize(mean)) 1:3: 1 b  1 1  -------------------------------------------------------  1:3: 2 b  2 2  -------------------------------------------------------  1:3: 3 b  4 4

also forums:

by(as.data.frame(mtcars[vars]), mtcars$am, dstats)

the problem function. if replace dstats mean or sd, still not work. works summary function. wonder how author got output in book?

source: https://forums.manning.com/posts/list/32059.page


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