To create combination of multiple vectors, we can use expand. grid function. For example, if we have six vectors say x, y, z, a, b, and c then the combination of vectors can be created by using the command expand.
To find the unique pair combinations of an R data frame column values, we can use combn function along with unique function.
The combn() function in R is used to return the combination of the elements of a given argument x taken m at a time.
expand. grid() function in R Language is used to create a data frame with all the values that can be formed with the combinations of all the vectors or factors passed to the function as argument.
this maybe what you are after
> expand.grid(a,b)
Var1 Var2
1 ABC 2012-05-01
2 DEF 2012-05-01
3 GHI 2012-05-01
4 ABC 2012-05-02
5 DEF 2012-05-02
6 GHI 2012-05-02
7 ABC 2012-05-03
8 DEF 2012-05-03
9 GHI 2012-05-03
10 ABC 2012-05-04
11 DEF 2012-05-04
12 GHI 2012-05-04
13 ABC 2012-05-05
14 DEF 2012-05-05
15 GHI 2012-05-05
If the resulting order isn't what you want, you can sort afterwards. If you name the arguments to expand.grid
, they will become column names:
df = expand.grid(a = a, b = b)
df[order(df$a), ]
And expand.grid
generalizes to any number of input columns.
The tidyr
package provides the nice alternative crossing
, which works better than the classic expand.grid
function because (1) strings are not converted into factors and (2) the sorting is more intuitive:
library(tidyr)
a <- c("ABC", "DEF", "GHI")
b <- c("2012-05-01", "2012-05-02", "2012-05-03", "2012-05-04", "2012-05-05")
crossing(a, b)
# A tibble: 15 x 2
a b
<chr> <chr>
1 ABC 2012-05-01
2 ABC 2012-05-02
3 ABC 2012-05-03
4 ABC 2012-05-04
5 ABC 2012-05-05
6 DEF 2012-05-01
7 DEF 2012-05-02
8 DEF 2012-05-03
9 DEF 2012-05-04
10 DEF 2012-05-05
11 GHI 2012-05-01
12 GHI 2012-05-02
13 GHI 2012-05-03
14 GHI 2012-05-04
15 GHI 2012-05-05
Missing in this r-faq overview is the CJ
-function from the data.table-package. Using:
library(data.table)
CJ(a, b, unique = TRUE)
gives:
a b 1: ABC 2012-05-01 2: ABC 2012-05-02 3: ABC 2012-05-03 4: ABC 2012-05-04 5: ABC 2012-05-05 6: DEF 2012-05-01 7: DEF 2012-05-02 8: DEF 2012-05-03 9: DEF 2012-05-04 10: DEF 2012-05-05 11: GHI 2012-05-01 12: GHI 2012-05-02 13: GHI 2012-05-03 14: GHI 2012-05-04 15: GHI 2012-05-05
NOTE: since version 1.12.2 CJ
autonames the resulting columns (see also here and here).
Since version 1.0.0, tidyr
offers its own version of expand.grid()
. It completes the existing family of expand()
, nesting()
, and crossing()
with a low-level function that works with vectors.
When compared to base::expand.grid()
:
Varies the first element fastest. Never converts strings to factors. Does not add any additional attributes. Returns a tibble, not a data frame. Can expand any generalised vector, including data frames.
a <- c("ABC", "DEF", "GHI")
b <- c("2012-05-01", "2012-05-02", "2012-05-03", "2012-05-04", "2012-05-05")
tidyr::expand_grid(a, b)
a b
<chr> <chr>
1 ABC 2012-05-01
2 ABC 2012-05-02
3 ABC 2012-05-03
4 ABC 2012-05-04
5 ABC 2012-05-05
6 DEF 2012-05-01
7 DEF 2012-05-02
8 DEF 2012-05-03
9 DEF 2012-05-04
10 DEF 2012-05-05
11 GHI 2012-05-01
12 GHI 2012-05-02
13 GHI 2012-05-03
14 GHI 2012-05-04
15 GHI 2012-05-05
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