How to apply mean function over elements of a list in R

Question

I have a list and I want to use lapply() to compute the mean of its elements. For example, for the seventh item of the list I have:

>list[[7]]
 [1] 1 1 1 1 1 1 1 1 1 1

and my output should be:

> mean(temp[[7]][1:10])
[1] 1

But when I use lapply() like below the result would be something else. What should I do?

> lapply(list[[7]][1:10],mean)
[[1]]
[1] 1

[[2]]
[1] 1
.
.
.
[[10]]
[1] 1

Answer 1

To get the mean of the 7th element of the list just use mean(list[[7]]). To get the mean of each element of the list use lapply(list,mean). And it's a really bad idea to call your list list.

Answer 2

consider using sapply instead of lapply.

# sample data
a<- 1:3
dat <- list(a, a*2, a*3)

# sapply gives a tidier output
> sapply(dat, mean)
[1] 2 4 6

> lapply(dat, mean)
[[1]]
[1] 2

[[2]]
[1] 4

[[3]]
[1] 6

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Also, you might want to take a look at the plyr package. This question also does a good job of explaining the different *apply functions