Generating all possible outcomes in r-CodePudding

Given a vector with numeric values, how do I generate all possible outcomes for subtraction to find the differences and put them in a data.frame?

dataset1 <- data.frame(numbers = c(1,2,3,4,5,6,7,8,9,10))

i.e. (1 - 1, 1 - 2 , 1 - 3,...)

Ideally, I would want the output to give me a data frame with 3 columns (Number X, Number Y, Difference) using dataset1.

CodePudding user response：

The expand.grid function can get you "pairings" which are different than the pairings you get with combn. Since you included 1-1 I'm assuming you didn't want since it doesn't return 1-1 and only gives you 45 combinations.

> pairs=expand.grid(X=1:10, Y=1:10)
> pairs$diff <- with(pairs, X-Y)
> pairs
     X  Y diff
1    1  1    0
2    2  1    1
3    3  1    2
4    4  1    3
5    5  1    4
6    6  1    5
7    7  1    6
8    8  1    7
9    9  1    8
10  10  1    9
11   1  2   -1
12   2  2    0
13   3  2    1
14   4  2    2
15   5  2    3
16   6  2    4
17   7  2    5
snipped remainder (total of 100 rows)

Use outer as another way to get such a group of paired differences;

> tbl <- matrix( outer(X=1:10, Y=1:10, "-"), 10, dimnames=list(X=1:10, Y=1:10))
> tbl
    Y
X    1  2  3  4  5  6  7  8  9 10
  1  0 -1 -2 -3 -4 -5 -6 -7 -8 -9
  2  1  0 -1 -2 -3 -4 -5 -6 -7 -8
  3  2  1  0 -1 -2 -3 -4 -5 -6 -7
  4  3  2  1  0 -1 -2 -3 -4 -5 -6
  5  4  3  2  1  0 -1 -2 -3 -4 -5
  6  5  4  3  2  1  0 -1 -2 -3 -4
  7  6  5  4  3  2  1  0 -1 -2 -3
  8  7  6  5  4  3  2  1  0 -1 -2
  9  8  7  6  5  4  3  2  1  0 -1
  10 9  8  7  6  5  4  3  2  1  0

But I didn't see a compact way to create a dataframe of the sort you specified.

The now deleted comment by @RitchieSacramento iswas correct:

> tbl <- matrix( outer(X=1:10, Y=1:10, "-"), 10, dimnames=list(X=1:10, Y=1:10))
> as.data.frame.table(tbl)
     X  Y Freq
1    1  1    0
2    2  1    1
3    3  1    2
4    4  1    3
5    5  1    4
6    6  1    5
7    7  1    6
8    8  1    7
9    9  1    8
10  10  1    9
11   1  2   -1
12   2  2    0
13   3  2    1
14   4  2    2
15   5  2    3
16   6  2    4

CodePudding user response：

You can use the combn() function to generate the list of all combinations take 2 at a time.

numbers = c(1,2,3,4,5,6,7,8,9,10)
output <-combn(numbers, 2, FUN = NULL, simplify = TRUE )

answer <- as.data.frame(t(output))
answer$Difference <- answer[ ,1] - answer[ ,2]

head(answer)

V1 V2 Difference
1  1  2         -1
2  1  3         -2
3  1  4         -3
4  1  5         -4
5  1  6         -5
6  1  7         -6