BIN - 9 months ago 53

R Question

I have a 3 ways frequency table, I want to combine them into a list, normally I write

`listOfTable <- list(table[,,1],table[,,2],table[,,3],table[,,4],table[,,5])`

`lapply`

`df <- data.frame(ID = c(rep(c("A","B","C"),5)),`

N = c(rep(c("1","2","3"),5)),

M = c(rep(1,3),rep(2,3),rep(3,3),rep(4,3),rep(5,3)))

applyAlist <- table(df$ID,df$N,df$M)

listOfTable <- list(applyAlist[,,1],applyAlist[,,2],applyAlist[,,3],applyAlist[,,4],applyAlist[,,5])

Answer

We can do this with `lapply`

by looping through the sequence of the third dimension and subsetting the 'applyAlist' based on the sequence.

```
lapply(seq(dim(applyAlist)[3]), function(i) applyAlist[,,i])
```

As the OP wants a `list`

output, `lapply`

always gives that output. With `sapply`

, the default option is `simplify = TRUE`

so it would return a `matrix`

or `vector`

when the `length`

of the elements are the same in case we did not change the option to `simplify = FALSE`

. In cases where the `list`

elements are of different `class`

es, this will become more noticeable and is damaging.

```
lst <- list(a = 1:3, b = rep(letters[1:3], 2), c = 2:4)
lapply(lst, unique)
#$a
#[1] 1 2 3
#$b
#[1] "a" "b" "c"
#$c
#[1] 2 3 4
sapply(lst, unique)
# a b c
#[1,] "1" "a" "2"
#[2,] "2" "b" "3"
#[3,] "3" "c" "4"
```

but,

```
sapply(lst, unique, simplify = FALSE)
#$a
#[1] 1 2 3
#$b
#[1] "a" "b" "c"
#$c
#[1] 2 3 4
```

gives similar results as `lapply`

as we changed the `simplify`

Source (Stackoverflow)