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mean of a column in a list of data frames

3 messages · Brandon Payne, Duncan Murdoch, Rui Barradas

Brandon Payne
# 
I have a list of data frames,

    ownersList <- list(exp2004owners,exp2005owners,
                   exp2006owners,exp2007owners,
                   exp2008owners,exp2009owners,
                   exp2010owners,exp2011owners,
                   exp2012owners,exp2013owners,
                   exp2014owners)

 I want to take the mean of the first column $grossIncome.
 I can access the first column with

lapply(ownersList, "[[", 1)                      ##works

But I can't take the mean of that.
mean(lapply(ownersList, "[[", 1))          ##not working

There must be a more idiomatic way to write this with map or apply.

ownersIncome<- c(mean(ownersList[[1]]$grossIncome),
                 mean(ownersList[[2]]$grossIncome),
                 mean(ownersList[[3]]$grossIncome),
                 mean(ownersList[[4]]$grossIncome),
                 mean(ownersList[[5]]$grossIncome),
                 mean(ownersList[[6]]$grossIncome),
                 mean(ownersList[[7]]$grossIncome),
                 mean(ownersList[[8]]$grossIncome),
                 mean(ownersList[[9]]$grossIncome),
                 mean(ownersList[[10]]$grossIncome),
                 mean(ownersList[[11]]$grossIncome))

I tried a for loop, which also didn't work.

aList<-
    for(i in 1:3){
    mean(ownersList[[i]]$grossIncome)
}
aList
Duncan Murdoch
#
On 05/02/2017 7:01 AM, Brandon Payne wrote:
lapply returns a list of the first columns, and mean() doesn't know what 
to do with that.
Yes, take the mean inside lapply:

lapply(ownersList, function(x) mean(x[[1]]))

Not tested.

Duncan Murdoch
for loops don't have a useful value:  it's always NULL.  This would have 
worked as

aList <- list()
for(i in 1:3){
     aList[[i]] <- mean(ownersList[[i]]$grossIncome)
}


Duncan Murdoch
Rui Barradas
# 
Hello,

Try instead the following.

aList<- numeric(3)
for(i in 1:3){
       aList[i] <- mean(ownersList[[i]]$grossIncome)
}
aList

Hope this helps,

Rui Barradas


Em 05-02-2017 12:01, Brandon Payne escreveu: