apply multiple functions in sapply

Question

I have a list of .stat files in tmp directory.

sample:

a.stat=>

abc,10

abc,20

abc,30

b.stat=>

xyz,10

xyz,30

xyz,70

and so on

I need to find summary of all .stat files. Currently I am using filelist<-list.files(path="/tmp/",pattern=".stat")

data<-sapply(paste("/tmp/",filelist,sep=''), read.csv, header=FALSE)

However I need to apply summary to all files being read. Or simply in n number of .stat files I need summary from 2nd column column

using

data<-sapply(paste("/tmp/",filelist,sep=''), summary, read.csv, header=FALSE) does not work and gives me summary with class character, which is no what I intend.

sapply(filelist, function(filename){df <- read.csv(filename, header=F);print(summary(df[,2]))}) works fine. However my overall objective is to find values that are more than 2 standard deviations away on either side (outliers). So I use sd, but at the same time need to check if all values in the file currently read come under 2SD range.

Answer 1

To apply multiple functions at once:

f <- function(x){
  list(sum(x),mean(x))
}
sapply(x, f)

In your case you want to apply them sequentially, so first read csv data then do summary:

sapply(lapply(paste("/tmp/",filelist,sep=''), read.csv), summary)

To subset your datasets to run summary on particular column you can use change outer sapply function from summary to function(x) summary(x[[2]]).