CODEWITHSUNDEEP
r
lovetl2002
lovetl2002

Reputation: 1058

How to create a data.frame/matrix like what aggregate() does?

Using aggregate(), I can get a data.frame like this:

  V1 V2   V3
1  1  2    1
2  1  3 2, 3
3  1  4    4
4  1  5 5, 6
5  1  6    7

For V3, it's list of vectors.

> b1$V3
$`0`
[1] 1

$`1`
[1] 2 3

$`2`
[1] 4

$`3`
[1] 5 6

$`4`
[1] 7

That surprised me since I was thinking that data.frame only have two dimensions. I can even convert it to a matrix which is pseudo-three-dimensional (though it's not real three-dimensional).

> as.matrix(b1)
     V1 V2 V3       
[1,] 1  2  1        
[2,] 1  3  Numeric,2
[3,] 1  4  4        
[4,] 1  5  Numeric,2
[5,] 1  6  7

However, I failed to create this kind of data structure in a regular way like adding a list to a data.frame/matrix. Since this kind of structure is helpful, I'd like know how it was created. Any ideas?

Upvotes: 0

Views: 61

Answers (1)

A5C1D2H2I1M1N2O1R2T1
A5C1D2H2I1M1N2O1R2T1

Reputation: 193517

This kind of structure can be made using the I function. 

mydf <- data.frame(
  a = 1:3,
  b = I(list(1, 3:5, 6:10))
)
str(mydf)
# 'data.frame':  3 obs. of  2 variables:
#  $ a: int  1 2 3
#  $ b:List of 3
#   ..$ : num 1
#   ..$ : int  3 4 5
#   ..$ : int  6 7 8 9 10
#   ..- attr(*, "class")= chr "AsIs"
as.matrix(mydf)
#      a b        
# [1,] 1 1        
# [2,] 2 Integer,3
# [3,] 3 Integer,5

You can also do this by adding the columns manually:

mydf2 <- data.frame(a = 1:3)
mydf2$b <- list(1, 3:5, 6:10)
str(mydf2)
as.matrix(mydf2)

Upvotes: 2

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