[R] mean of a column in a list of data frames
Duncan Murdoch
murdoch.duncan at gmail.com
Sun Feb 5 13:15:46 CET 2017
On 05/02/2017 7:01 AM, Brandon Payne wrote:
> 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 $grossIncome.
> I can access the first column with
>
> lapply(ownersList, "[[", 1) ##works
>
> But I can't take the mean of that.
> mean(lapply(ownersList, "[[", 1)) ##not working
lapply returns a list of the first columns, and mean() doesn't know what
to do with that.
>
> There must be a more idiomatic way to write this with map or apply.
Yes, take the mean inside lapply:
lapply(ownersList, function(x) mean(x[[1]]))
Not tested.
Duncan Murdoch
>
> ownersIncome<- c(mean(ownersList[[1]]$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]]$grossIncome)
> }
for loops don't have a useful value: it's always NULL. This would have
worked as
aList <- list()
for(i in 1:3){
aList[[i]] <- mean(ownersList[[i]]$grossIncome)
}
Duncan Murdoch
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