Nov 14, 2018
Get the chance to pre-order new collection at the best price
http://leesle.kr/product-category/outer/
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Get the chance to pre-order new collection at the best price
http://leesle.kr/product-category/outer/
Get the chance to pre-order new collection at the best price
http://leesle.kr/product-category/outer/
R function of the day #003
outer() The math inclined know about it but some don't think of it enough. I know I didn't! Slightly generalizing the outer product to arbitrary functions is useful. A typical use is to make a high dimension tensor.
> x1=matrix(1:6,ncol=3) > x2=matrix(1:4,ncol=2) > outer(x1,x2) , , 1, 1 [,1] [,2] [,3] [1,] 1 3 5 [2,] 2 4 6 , , 2, 1 [,1] [,2] [,3] [1,] 2 6 10 [2,] 4 8 12 , , 1, 2 [,1] [,2] [,3] [1,] 3 9 15 [2,] 6 12 18 , , 2, 2 [,1] [,2] [,3] [1,] 4 12 20 [2,] 8 16 24
Pairwise combinations: Who doesn't want to make matrices like this when it is so quick and easy?
> outer(1:4,LETTERS[3:9],function(n,l) paste(n,l,sep="")) [,1] [,2] [,3] [,4] [,5] [,6] [,7] [1,] "1C" "1D" "1E" "1F" "1G" "1H" "1I" [2,] "2C" "2D" "2E" "2F" "2G" "2H" "2I" [3,] "3C" "3D" "3E" "3F" "3G" "3H" "3I" [4,] "4C" "4D" "4E" "4F" "4G" "4H" "4I"
A final example (with apologies for being so hetero-normative)
>girls=c( "Sookie", 'Tara', 'Arlene', "Jessica", "Pam", "Alcide Herveaux", "Holly", "Luna", "Nan", "Maxine", "Lettie Mae", "Maryann", "Rene", "Crystal", "Debbie") >boys=c( "Bill", "Sam", "Jason", "Andy", "Lafayette", "Hoyt", "Eric", "Terry", "Sheriff Bud", "Steve", "Jesus", "Tommy", 'Russell', "Mike ", "Eggs") >outer(boys,girls,paste) ...output omitted...