combining head and tail methods in R

Question

I use the head(d) and tail(d) methods in R package utils a lot - frequently one after the other. So I wrote a simple wrapper for the two functions: ``` ht <- function(d, m=5, n=m){ # print the head and tail together cat(" head --> ", head(d,m), " ", "--------", " ", "tail --> ", tail(d,n), " ") } ``` And I got some unexpected results. Can someone please help me understand why? (so i can fix it or at least understand your solution!). Some background... Numeric values work fine: ``` x <- 1:100 ht(x) ``` So does complex: ``` ni <- as.complex(1:100) ht(ni) ``` and characters: ``` ll <- letters[1:26] ht(ll) ``` Matrix loses it's structure, returning [1,1] to [5,5] + [16,1] to [20,5] but as two vectors -- compare: ``` m <- matrix(1:10, 20) ht(m) ``` to: ``` head(m, 5) tail(m,5) ``` I would like to keep the matrix structure, as the utils methods does - is this possible? Finally (well, there may be more bugs, this is just where I'm up to) data.frames are a mess: ``` df <- data.frame(num=x[…

Accepted Answer

Why not modify your function to output a list instead?

```
ht <- function(d, m=5, n=m){
  # print the head and tail together
  list(HEAD = head(d,m), TAIL = tail(d,n))
}
```

Here's the output for your `matrix` and `data.frame`:

```
ht(matrix(1:10, 20))
# $HEAD
#      [,1]
# [1,]    1
# [2,]    2
# [3,]    3
# [4,]    4
# [5,]    5
# 
# $TAIL
#       [,1]
# [16,]    6
# [17,]    7
# [18,]    8
# [19,]    9
# [20,]   10

ht(data.frame(num=x[1:26], char=ll))
# $HEAD
#   num char
# 1   1    a
# 2   2    b
# 3   3    c
# 4   4    d
# 5   5    e
# 
# $TAIL
#    num char
# 22  22    v
# 23  23    w
# 24  24    x
# 25  25    y
# 26  26    z
```

combining head and tail methods in R

Solution

Problem