Sum of subvectors of a vector in R

Question

Given a vector x of length k, I would like to obtain a k by k matrix X where X[i,j] is the sum of x[i] + ... + x[j]. The

Answer 1

You can also try this:

x <- 1:10

matrix(apply(expand.grid(1:10, 1:10), 1, function(y) sum(x[y[2]:y[1]])), 10, 10)
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
 [1,]    1    3    6   10   15   21   28   36   45    55
 [2,]    3    2    5    9   14   20   27   35   44    54
 [3,]    6    5    3    7   12   18   25   33   42    52
 [4,]   10    9    7    4    9   15   22   30   39    49
 [5,]   15   14   12    9    5   11   18   26   35    45
 [6,]   21   20   18   15   11    6   13   21   30    40
 [7,]   28   27   25   22   18   13    7   15   24    34
 [8,]   36   35   33   30   26   21   15    8   17    27
 [9,]   45   44   42   39   35   30   24   17    9    19
[10,]   55   54   52   49   45   40   34   27   19    10