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I have a simple matrix like:
> a = matrix(c(c(1:10),c(10:1)), ncol=2) > a [,1] [,2] [1,] 1 10 [2,] 2 9 [3,] 3 8 [4,] 4 7 [5,] 5 6 [6,] 6 5 [7,] 7 4 [8,] 8 3 [9,] 9 2 [10,] 10 1 I would like to get this result:
[,1] [,2] [1,] 10 1 [2,] 9 2 [3,] 8 3 [4,] 7 4 [5,] 6 5 [6,] 5 6 [7,] 4 7 [8,] 3 8 [9,] 2 9 [10,] 1 10 The exact reverse of the matrix. How can I get it? Thanks
966
The rev() method reverses the order of the matrix on the basis of columns.
To find the inverse of a 2x2 matrix: swap the positions of a and d, put negatives in front of b and c, and divide everything by the determinant (ad-bc).
To reverse column order in a matrix, we make use of the numpy. fliplr() method. The method flips the entries in each row in the left/right direction. Column data is preserved but appears in a different order than before.
Reversing the rows of a data frame in pandas can be done in python by invoking the loc() function. The panda's dataframe. loc() attribute accesses a set of rows and columns in the given data frame by either a label or a boolean array.
a[nrow(a):1,] # [,1] [,2] # [1,] 10 1 # [2,] 9 2 # [3,] 8 3 # [4,] 7 4 # [5,] 6 5 # [6,] 5 6 # [7,] 4 7 # [8,] 3 8 # [9,] 2 9 # [10,] 1 10 Try rev with apply:
> a <- matrix(c(1:10,10:1), ncol=2) > a [,1] [,2] [1,] 1 10 [2,] 2 9 [3,] 3 8 [4,] 4 7 [5,] 5 6 [6,] 6 5 [7,] 7 4 [8,] 8 3 [9,] 9 2 [10,] 10 1 > b <- apply(a, 2, rev) > b [,1] [,2] [1,] 10 1 [2,] 9 2 [3,] 8 3 [4,] 7 4 [5,] 6 5 [6,] 5 6 [7,] 4 7 [8,] 3 8 [9,] 2 9 [10,] 1 10 If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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