how to `combn` every combination of every element of a vector into a single list

Question

I failed at searching for how to do this specific transformation. Does anyone have a smart way to achieve this? sorry if I missed an obvious answer somewhere. thanks

# start with a single vector
1:3

# achieve this desired structure, containing every combination
# from combn( x , 1 ) thru combn( x , length( x ) )
list(
    1 ,
    2 , 
    3 ,
    c( 1 , 2 ) ,
    c( 1 , 3 ) ,
    c( 2 , 3 ) ,
    c( 1 , 2 , 3 )
)

akrun · Answer 1 · 2018-12-07T14:36:03.430

2

Loop through the sequence of values, get the combn of the vector with m specified as the sequence values, split by 'col', flatten the nested list to a list of vectors with do.call(c and unname it

unname(do.call(c, lapply(1:3, function(x) {
      x1 <- combn(1:3, x)
      split(x1, col(x1))})))
#[[1]]
#[1] 1

#[[2]]
#[1] 2

#[[3]]
#[1] 3

#[[4]]
#[1] 1 2

#[[5]]
#[1] 1 3

#[[6]]
#[1] 2 3

#[[7]]
#[1] 1 2 3

Or as @IceCreamToucan mentioned in the comments

do.call(c, lapply(1:3, function(x) combn(1:3, x, simplify = FALSE)))

edited Dec 07 '18 at 14:36

answered Dec 07 '18 at 14:33

akrun

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1

Nice! You can simplify the function to `function(x) combn(1:3, x, simplify = F)` – IceCreamToucan Dec 07 '18 at 14:34
@IceCreamToucan Thanks, that is so compact. I forgot the `simplify` argument. – akrun Dec 07 '18 at 14:36
1

thanks! maybe it should be `myfun <- function( w ) do.call(c, lapply(seq(w), function(x) combn(w, x, simplify = FALSE)))` so it works on character vectors? – Anthony Damico Dec 07 '18 at 14:41
@AnthonyDamico Yeah, I think `seq_along(w)` would be slightly faster. Haven't checked it – akrun Dec 07 '18 at 14:43

how to `combn` every combination of every element of a vector into a single list

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