How to convert a list of vectors with various length into a Data Frame

Question

By using as.data.frame() is it easy if it works.

Example:

Input

d1<-list(A=c(1,2,3),B=c(4,5,6,7,8))

Output

   A B
1  1 4
2  2 5
3  3 6
4 NA 7
5 NA 8

A and B are the colnames of the data.frame.

One possible case is sapply(d1, '[', seq(max(sapply(d1, length)))), but it's also complex.

Answer 1

We can easily use this command

as.data.frame(lapply(d1, "length<-",max(lengths(d1))))

Comments

Could you please explain what does this syntax mean:

"length<-"

Thank you in advance.

---

In the above code, length <- set the length of vectors (including lists) and factors, and of any other R object

length<-"max(lengths(d1)) set the length of both the list elements as the maximum length of list elements.

> length(d1$A)
[1] 3
> length(d1$B)
[1] 5
> length<-max(lengths(d1))
> length
[1] 5

Then lappy returns a list of the same length by adding extra NA at index with no elements. as.data.frame later converts the list into a data frame.

> lapply(d1, "length<-",max(lengths(d1)))
$A
[1]  1  2  3 NA NA

$B
[1] 4 5 6 7 8

I hope it helps.

---

Thank you very much indeed, I know generally what lenght() function can do, but this syntax

"length<-",  I have never seen before (I am R-beginner). Do you have maybe more examples how to use such a code, I mean assignment operator <- in quotes like this one: 

"length<-"

best wishes

---

Hey Andrzej,

A few functions like class, names, etc also allow <- within " ".

I have not used them before, but you can try and share your thoughts.