在 data.table 上应用 function 并将结果存储在列表中

Question

I have a data.table with the following format:

ColName  xvalue   yvalue

Column1  5       10
Column2  3        5
Column3  2        4

I have defined a function as follows:

opt <- function (x,y){
return(x+y)
}

I want to apply the function over each row of the data.table and store the resulting value in a list like below:

x
$column1
[1]15

$column2
[1]8

$column3
[1]6

Essentially I am applying a function that takes each row of the data.table as input parameters and stores the output as members of a list. Is there a data.table way of doing this? Thanks!

Answer 1

You can simply do,

split(rowSums(df[-1]), df$ColName)

#$Column1
#[1] 15

#$Column2
#[1] 8

#$Column3
#[1] 6

Answer 2

An option is to apply the opt and then use as.list

with(df1, as.list(setNames(opt(xvalue, yvalue), ColName)))
#$Column1
#[1] 15

#$Column2
#[1] 8

#$Column3
#[1] 6

data

df1 <- structure(list(ColName = c("Column1", "Column2", "Column3"), 
    xvalue = c(5L, 3L, 2L), yvalue = c(10L, 5L, 4L)), 
    class = "data.frame", row.names = c(NA, 
-3L))

Answer 3

You can use Map to get output as list:

setNames(Map(opt, df$xvalue, df$yvalue), df$ColName)

#$Column1
#[1] 15

#$Column2
#[1] 8

#$Column3
#[1] 6