如何在 r 中的列表上应用特定函数？

Question

Good morning!

Suppose i have the following list in r :

l=list(c(1,2,30),c(5,5,5))

My question is very simple but I failed to get the right answer !

How can i apply a function over rows/columns to get the following outputs :

l_sum_of_rows=list(33,15)

l_sum_of_columns=list(6,7,35)

Such things are very easy to acheive with matrices . However , I don't know how to do same with lists.

Thank you for help in advance !

Answer 1

If you think of your data as rows and columns, you should make that list a data.frame. Anyway, the first task is easy with lapply :

sapply(l, sum)
#[1] 33 15

For the second task you can use do.call if you have a length-two list:

do.call("+", l)
#[1]  6  7 35

For longer lists, you can use Reduce :

Reduce("+", l)
#[1]  6  7 35

Answer 2

Lists of vectors of equal length are (almost) data.frames and there is a lot of specialty functions for those.

l <- list(c(1,2,30),c(5,5,5))
ld <- as.data.frame(l)
rowSums(ld)   # sums of rows
colSums(ld)   # sums of columns