[R] Why does aggregate fail?

[James Rome]

I am trying to get hourly totals, given 15-minute bins.
s = seq(0, 95, 1)
s = floor(s/4)   # 0  0  0  0  1  1  1  1  2  2  2  2  3  3  3  3  4 . . .

> s
 [1]  0  0  0  0  1  1  1  1  2  2  2  2  3  3  3  3  4  4  4  4  5  5 
5  5  6
[26]  6  6  6  7  7  7  7  8  8  8  8  9  9  9  9 10 10 10 10 11 11 11
11 12 12
[51] 12 12 13 13 13 13 14 14 14 14 15 15 15 15 16 16 16 16 17 17 17 17
18 18 18
[76] 18 19 19 19 19 20 20 20 20 21 21 21 21 22 22 22 22 23 23 23 23

> mode(d)
[1] "list"
> d
       0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
25 26
Sunday 0 1 0 0 0 0 0 0 0 0  0  0  0  0  0  0  0  2  0  0  0  0  0  0  0 
0  0
       27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
49 50
Sunday  0  0  0  0  0  5  5  5  0  0  0  0  0  0  0  6  0  3  1  0  1 
6  8  9
       51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
73 74
Sunday  7  9 10  5  0  1  0  1  1  1  0  0  0  1  0  0  7 10  9  9 11
11  8  8
       75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
Sunday 10  7  6  7  8  7  4  4  6  5  5  5  5  0  0  0  1  6  2  3  0
> x = aggregate(d, by=list(s), FUN="sum")
Error in FUN(X[[1L]], ...) : arguments must have same length
> length(s)
[1] 96
> length(d)
[1] 96

What am I doing wrong?

Thanks in advance list,
Jim Rome