# [R] sapply following using by with a list of factors

Frank E Harrell Jr f.harrell at vanderbilt.edu
Mon May 30 13:34:33 CEST 2005

```McClatchie, Sam (PIRSA-SARDI) wrote:
> Background:
> OS: Linux Mandrake 10.1
> release: R 2.0.0
> editor: GNU Emacs 21.3.2
> front-end: ESS 5.2.3
> ---------------------------------
> Colleagues
>
> I am having some trouble extracting results from the function by, used to
> average variables in a data.frame first by one factor (depth) and then by a
> second factor (station). The real data.frame is quite large
>
>>dim(data.2001)
>
> [1] 32049  11
>
> Here is a snippet of code:
>
> ## bin density data for each station into 1 m depth bins, containing means
>     data.2001.test\$integer.Depth <- as.factor(round(data.2001.test\$Depth,
> digits=0))
>     attach(data.2001.test)
>     binned.data.2001 <- by(data.2001.test[,5:11], list(depth=integer.Depth,
> station=Station), mean)
>
> and here is a snippet of the data.frame
>
>
>>dim(data.2001.test)
>
> [1] 150  11
>
>>dump("data.2001.test", file=stdout())
>
> data.2001.test <-
> structure(list(Cruise = structure(as.integer(c(1, 1, 1, 1, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)), .Label =
> "Ngerin01", class = "factor"),
>     Station = structure(as.integer(c(2, 2, 2, 2, 2, 2, 2, 2,
>     2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
>     2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
>     2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
>     3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
>     3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
>     3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
>     4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
>     4, 4, 4, 4, 4, 4, 4, 5, 5)), .Label = c("a1", "a2", "a3",
>     "a4", "a5", "a6", "a7", "a8", "a9", "b1", "b2", "b3", "b4",
>     "b5", "b6", "b7", "c1", "c2", "c3", "c4", "c5", "c6", "c7",
>     "d1", "d2", "d3", "d4", "d5", "d6", "e1", "e2", "e3", "e4",
>     "e5", "e6", "e7", "f1", "f2", "f3", "f4", "f5", "f6", "f7",
>     "f8", "f9", "g1", "g10", "g11", "g2", "g3", "g4", "g5", "g6",
>     "g7", "g8", "g9", "gsvc1", "gsvc2", "gsvc3", "gsvc4", "gsvc5",
>     "gsvc6", "gsvc7", "gsvc8", "gsvc9", "gsvd1", "gsvd2", "gsvd3",
>     "gsvd4", "gsvd5", "gsvd6", "gsvd7", "gsvd8", "h1", "h11",
>     "h2", "h3", "h4", "h5", "h6", "h7", "h8", "h9", "i1", "i10",
>     "i2", "i3", "i4", "i5", "i6", "i7", "i8", "i9", "j1", "j10",
>     "j2", "j3", "j4", "j5", "j6", "j7", "j8", "j9", "k1", "k10",
>     "k2", "k3", "k4", "k5", "k6", "k7", "k8", "k9", "l1", "l10",
>     "l11", "l12", "l2", "l3", "l4", "l5", "l6", "l7", "l8", "l9",
>     "m1", "m10", "m11", "m2", "m3", "m4", "m5", "m6", "m7", "m8",
>     "m9", "mx", "n1", "n10", "n11", "n2", "n3", "n4", "n5", "n6",
>     "n7", "n8", "n9", "nx", "o1", "o10", "o11", "o13", "o2",
>     "o3", "o4", "o5", "o6", "o7", "o8", "o9", "ox", "p10", "p11",
>     "p2", "p3", "p4", "p5", "p6", "p7", "p8", "p9", "px", "q1",
>     "q10", "q11", "q12", "q13", "q2", "q3", "q4", "q5", "q6",
>     "q7", "q8", "q9", "qx", "r1", "r10", "r11", "r12", "r13",
>     "r14", "r15", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9",
>     "rx", "s1", "s10", "s11", "s12", "s13", "s14", "s15", "s16",
>     "s2", "s3", "s4", "s5", "s6", "s7", "s8", "s9", "sgc1", "sgc2",
>     "sgc3", "sgc4", "sgc5", "sgc6", "sgc7", "sx", "t1", "t10",
>     "t11", "t12", "t13", "t14", "t15", "t16", "t2", "t3", "t4",
>     "t5", "t6", "t7", "t8", "t9", "tx", "u1", "u10", "u11", "u12",
>     "u13", "u14", "u15", "u2", "u3", "u4", "u5", "u6", "u7",
>     "u8", "u9", "ux", "v1", "v10", "v11", "v2", "v3", "v4", "v5",
>     "v6", "v7", "v8", "v9", "vx", "w2", "w3", "w4", "w5", "w6",
>     "w7", "w8", "w9", "wx", "x2", "x3", "x4", "x5", "x6", "x7",
>     "x8"), class = "factor"), Lon = c(138.421, 138.421, 138.421,
>     138.421, 138.421, 138.421, 138.421, 138.421, 138.421, 138.421,
>     138.421, 138.421, 138.421, 138.421, 138.421, 138.421, 138.421,
>     138.421, 138.421, 138.421, 138.421, 138.421, 138.421, 138.421,
>     138.421, 138.421, 138.421, 138.421, 138.421, 138.421, 138.421,
>     138.421, 138.421, 138.421, 138.421, 138.421, 138.421, 138.421,
>     138.421, 138.421, 138.421, 138.421, 138.421, 138.421, 138.421,
>     138.421, 138.421, 138.421, 138.421, 138.421, 138.421, 138.421,
>     138.421, 138.421, 138.352, 138.352, 138.352, 138.352, 138.352,
>     138.352, 138.352, 138.352, 138.352, 138.352, 138.352, 138.352,
>     138.352, 138.352, 138.352, 138.352, 138.352, 138.352, 138.352,
>     138.352, 138.352, 138.352, 138.352, 138.352, 138.352, 138.352,
>     138.352, 138.352, 138.352, 138.352, 138.352, 138.352, 138.352,
>     138.352, 138.352, 138.352, 138.352, 138.352, 138.352, 138.352,
>     138.352, 138.352, 138.352, 138.352, 138.352, 138.352, 138.352,
>     138.352, 138.352, 138.352, 138.352, 138.352, 138.352, 138.277,
>     138.277, 138.277, 138.277, 138.277, 138.277, 138.277, 138.277,
>     138.277, 138.277, 138.277, 138.277, 138.277, 138.277, 138.277,
>     138.277, 138.277, 138.277, 138.277, 138.277, 138.277, 138.277,
>     138.277, 138.277, 138.277, 138.277, 138.277, 138.277, 138.277,
>     138.277, 138.277, 138.277, 138.277, 138.277, 138.277, 138.277,
>     138.277, 138.277, 138.277, 138.277, 138.277, 138.201, 138.201
>     ), Lat = c(-35.766, -35.766, -35.766, -35.766, -35.766, -35.766,
>     -35.766, -35.766, -35.766, -35.766, -35.766, -35.766, -35.766,
>     -35.766, -35.766, -35.766, -35.766, -35.766, -35.766, -35.766,
>     -35.766, -35.766, -35.766, -35.766, -35.766, -35.766, -35.766,
>     -35.766, -35.766, -35.766, -35.766, -35.766, -35.766, -35.766,
>     -35.766, -35.766, -35.766, -35.766, -35.766, -35.766, -35.766,
>     -35.766, -35.766, -35.766, -35.766, -35.766, -35.766, -35.766,
>     -35.766, -35.766, -35.766, -35.766, -35.766, -35.766, -35.827,
>     -35.827, -35.827, -35.827, -35.827, -35.827, -35.827, -35.827,
>     -35.827, -35.827, -35.827, -35.827, -35.827, -35.827, -35.827,
>     -35.827, -35.827, -35.827, -35.827, -35.827, -35.827, -35.827,
>     -35.827, -35.827, -35.827, -35.827, -35.827, -35.827, -35.827,
>     -35.827, -35.827, -35.827, -35.827, -35.827, -35.827, -35.827,
>     -35.827, -35.827, -35.827, -35.827, -35.827, -35.827, -35.827,
>     -35.827, -35.827, -35.827, -35.827, -35.827, -35.827, -35.827,
>     -35.827, -35.827, -35.827, -35.883, -35.883, -35.883, -35.883,
>     -35.883, -35.883, -35.883, -35.883, -35.883, -35.883, -35.883,
>     -35.883, -35.883, -35.883, -35.883, -35.883, -35.883, -35.883,
>     -35.883, -35.883, -35.883, -35.883, -35.883, -35.883, -35.883,
>     -35.883, -35.883, -35.883, -35.883, -35.883, -35.883, -35.883,
>     -35.883, -35.883, -35.883, -35.883, -35.883, -35.883, -35.883,
>     -35.883, -35.883, -35.95, -35.95), Depth = c(5.092, 5.289,
>     5.584, 5.78, 6.075, 6.37, 6.665, 7.156, 7.451, 7.845, 8.238,
>     8.533, 8.729, 8.926, 9.123, 9.319, 9.614, 10.106, 10.499,
>     10.991, 11.58, 12.17, 12.76, 13.35, 13.94, 14.53, 15.119,
>     15.709, 16.201, 16.594, 16.987, 17.282, 17.577, 18.069, 18.364,
>     18.659, 18.954, 19.15, 19.347, 19.543, 19.838, 20.232, 20.723,
>     21.215, 21.706, 22.394, 22.788, 23.082, 23.377, 23.574, 23.869,
>     24.262, 24.557, 24.95, 5.19, 5.584, 6.075, 6.567, 7.058,
>     7.55, 7.845, 8.14, 8.336, 8.729, 9.024, 9.516, 10.007, 10.597,
>     11.089, 11.777, 12.367, 12.858, 13.252, 13.645, 14.038, 14.333,
>     14.726, 15.021, 15.414, 16.004, 16.397, 16.987, 17.381, 17.872,
>     18.167, 18.462, 18.954, 19.445, 19.838, 20.428, 20.92, 21.51,
>     22.099, 22.591, 23.181, 23.574, 23.869, 23.869, 23.869, 23.967,
>     23.967, 24.066, 24.066, 24.262, 24.262, 24.36, 24.36, 5.387,
>     5.78, 5.977, 6.173, 6.468, 6.763, 7.156, 7.55, 8.041, 8.434,
>     9.024, 9.418, 9.811, 10.007, 10.302, 10.597, 10.991, 11.482,
>     11.875, 12.367, 12.858, 13.252, 13.645, 13.94, 14.333, 14.726,
>     15.218, 15.808, 16.397, 16.987, 17.479, 18.069, 18.659, 19.445,
>     19.937, 20.723, 21.215, 21.804, 22.198, 22.591, 22.984, 5.485,
>     5.977), Temperature.oC = c(19.743, 19.7421, 19.7396, 19.7354,
>     19.7162, 19.6801, 19.6181, 19.5434, 19.403, 19.2851, 19.2514,
>     19.2278, 19.2303, 19.2379, 19.248, 19.2227, 19.205, 19.2,
>     19.1941, 19.1907, 19.1856, 19.1772, 19.1662, 19.1561, 19.1493,
>     19.1434, 19.1383, 19.1341, 19.1282, 19.1172, 19.1096, 19.1113,
>     19.1189, 19.1451, 19.2152, 19.2641, 19.259, 19.2405, 19.2278,
>     19.2244, 19.2017, 19.1772, 19.1527, 19.0868, 18.6986, 18.2519,
>     17.9853, 17.871, 17.8237, 17.8366, 17.7143, 17.4717, 17.36,
>     17.3071, 19.6151, 19.6135, 19.6126, 19.6134, 19.6126, 19.6118,
>     19.6118, 19.6109, 19.6109, 19.6109, 19.6109, 19.6109, 19.6101,
>     19.6084, 19.6092, 19.61, 19.6092, 19.6075, 19.605, 19.5974,
>     19.5916, 19.5832, 19.5765, 19.5706, 19.5597, 19.5328, 19.5042,
>     19.4084, 19.2998, 19.1665, 18.9958, 18.8331, 18.6955, 18.6207,
>     18.5594, 18.4802, 18.4008, 18.3214, 18.2265, 18.1631, 18.1426,
>     18.1126, 18.1049, 18.062, 18.098, 18.11, 18.0286, 18.1117,
>     18.0989, 18.0989, 18.0114, 18.1152, 17.9513, 19.3769, 19.371,
>     19.3718, 19.3685, 19.344, 19.3137, 19.2269, 19.1036, 19.0013,
>     18.9488, 18.9082, 18.8573, 18.8268, 18.8157, 18.8124, 18.7996,
>     18.7674, 18.7198, 18.679, 18.6535, 18.6416, 18.6305, 18.611,
>     18.5922, 18.5514, 18.5139, 18.4934, 18.4841, 18.4968, 18.49,
>     18.4644, 18.4534, 18.4465, 18.4414, 18.4389, 18.4295, 18.4346,
>     18.4337, 18.4269, 18.4064, 18.4022, 19.3895, 19.3912), Salinity =
> c(35.166,
>     35.1667, 35.2001, 35.2246, 35.2577, 35.2959, 35.3443, 35.3771,
>     35.4354, 35.5, 35.4849, 35.5368, 35.532, 35.5466, 35.5127,
>     35.5236, 35.5294, 35.5402, 35.5438, 35.5451, 35.5453, 35.5417,
>     35.5442, 35.5473, 35.5476, 35.5484, 35.5526, 35.5453, 35.5409,
>     35.5409, 35.5565, 35.567, 35.5962, 35.7026, 35.7273, 35.6732,
>     35.6655, 35.6442, 35.6696, 35.6644, 35.66, 35.6623, 35.6751,
>     35.3696, 35.2176, 35.4344, 35.5435, 35.6172, 35.6572, 35.5419,
>     35.3845, 35.5031, 35.6039, 35.5771, 35.5487, 35.5421, 35.5584,
>     35.5746, 35.5923, 35.6046, 35.5229, 35.592, 35.5998, 35.626,
>     35.6298, 35.6309, 35.6341, 35.6432, 35.6463, 35.6466, 35.6458,
>     35.647, 35.649, 35.6514, 35.6496, 35.654, 35.6491, 35.6579,
>     35.6381, 35.645, 35.5544, 35.5725, 35.5076, 35.4342, 35.4509,
>     35.4715, 35.5495, 35.5413, 35.582, 35.5519, 35.5219, 35.4919,
>     35.5158, 35.5611, 35.553, 35.5694, 35.5706, 35.5304, 35.5371,
>     35.5565, 35.5527, 35.5686, 35.5947, 35.5688, 35.5104, 35.5478,
>     35.5164, 35.4598, 35.5322, 35.5115, 35.5196, 35.5457, 35.598,
>     35.651, 35.6238, 35.5903, 35.5912, 35.5766, 35.5761, 35.5781,
>     35.5903, 35.5944, 35.5731, 35.5405, 35.5652, 35.5627, 35.5872,
>     35.5879, 35.5772, 35.5738, 35.5589, 35.5497, 35.5779, 35.5766,
>     35.6047, 35.5866, 35.5559, 35.5738, 35.5778, 35.5808, 35.585,
>     35.5708, 35.5894, 35.5848, 35.5732, 35.5587, 35.5776, 35.5798,
>     35.5151, 35.5029), Fluoresence.Volts = c(0.6947, 0.6789,
>     0.6923, 0.6935, 0.6996, 0.7045, 0.6825, 0.6911, 0.6886, 0.685,
>     0.6801, 0.6874, 0.7009, 0.6996, 0.6935, 0.6899, 0.7045, 0.7106,
>     0.7082, 0.7021, 0.7009, 0.7375, 0.7302, 0.7253, 0.7436, 0.7692,
>     0.7741, 0.7814, 0.7619, 0.7851, 0.7961, 0.7998, 0.7851, 0.7863,
>     0.7998, 0.823, 0.8388, 0.8462, 0.8718, 0.8864, 0.895, 0.873,
>     0.8632, 0.9035, 0.9744, 1.0049, 1.0537, 1.1026, 1.1258, 1.1258,
>     1.1013, 1.0952, 1.072, 1.0488, 0.7265, 0.7241, 0.7143, 0.7326,
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>     0.7546, 0.7827, 0.7839, 0.7729, 0.7705, 0.7985, 0.8071, 0.8254,
>     0.8144, 0.8144, 0.8181, 0.8217, 0.8083, 0.8339, 0.8376, 0.8437,
>     0.8791, 0.8913, 0.9096, 0.9133, 0.9267, 0.928, 0.9158, 0.9609,
>     0.956, 0.9328, 0.9292, 0.9365, 0.9304, 0.9365, 0.9121, 0.917,
>     0.9158, 0.9109, 0.9206, 0.9048, 0.9096, 0.917, 0.9109, 0.9206,
>     0.9243, 0.7717, 0.7839, 0.7656, 0.7643, 0.801, 0.8217, 0.8352,
>     0.8523, 0.8852, 0.8864, 0.8889, 0.8706, 0.8877, 0.8913, 0.8864,
>     0.8901, 0.8864, 0.8962, 0.8938, 0.8901, 0.8803, 0.8999, 0.8974,
>     0.895, 0.8828, 0.8645, 0.884, 0.8889, 0.873, 0.8742, 0.8828,
>     0.8828, 0.8926, 0.8706, 0.8816, 0.8742, 0.8742, 0.8669, 0.8742,
>     0.8791, 0.8755, 0.7411, 0.7387), Density.kg.m3 = c(24.9796,
>     24.9812, 25.0087, 25.0293, 25.0609, 25.1008, 25.1553, 25.202,
>     25.2843, 25.3659, 25.3648, 25.4118, 25.4084, 25.4184, 25.3908,
>     25.4065, 25.4168, 25.4285, 25.4345, 25.4386, 25.4426, 25.4446,
>     25.452, 25.4595, 25.4641, 25.4689, 25.476, 25.4741, 25.4744,
>     25.479, 25.4946, 25.5035, 25.5251, 25.6019, 25.604, 25.5513,
>     25.548, 25.5374, 25.561, 25.5587, 25.5625, 25.5723, 25.5906,
>     25.3762, 25.3611, 25.6424, 25.794, 25.88, 25.9236, 25.8329,
>     25.7436, 25.8955, 26.0012, 25.9952, 25.3056, 25.3027, 25.3176,
>     25.3319, 25.3478, 25.3596, 25.2985, 25.3528, 25.3596, 25.3813,
>     25.3855, 25.3885, 25.3934, 25.4034, 25.4077, 25.4107, 25.4129,
>     25.4164, 25.4204, 25.4259, 25.4278, 25.4346, 25.4344, 25.4439,
>     25.4334, 25.4483, 25.3883, 25.4296, 25.4099, 25.3904, 25.4483,
>     25.5069, 25.6037, 25.6185, 25.6669, 25.6664, 25.6656, 25.6651,
>     25.7098, 25.7624, 25.7639, 25.7857, 25.7898, 25.7697, 25.7659,
>     25.7782, 25.7955, 25.7875, 25.8107, 25.7917, 25.7687, 25.772,
>     25.7886, 25.3006, 25.3591, 25.344, 25.3519, 25.3795, 25.4286,
>     25.4932, 25.506, 25.5088, 25.5246, 25.5264, 25.5408, 25.5518,
>     25.5648, 25.5701, 25.5584, 25.5434, 25.5765, 25.5867, 25.6141,
>     25.6198, 25.6161, 25.6202, 25.6149, 25.6199, 25.6526, 25.659,
>     25.6854, 25.671, 25.6518, 25.6741, 25.6826, 25.6892, 25.6972,
>     25.6891, 25.7092, 25.7065, 25.7005, 25.6928, 25.7142, 25.7187,
>     25.34, 25.3324), Brunt.Vaisala.Freq.cycl.h = c(15.222, 6.59496,
>     17.1348, 17.8131, 18.7135, 21.4038, 22.0582, 22.8786, 28.2346,
>     14.8181, 5.59839, 11.962, -5.12458, 7.09748, -16.0581, 1.9386,
>     10.7242, 7.05743, 5.22594, 3.27465, 1.23835, 0.574964, 5.06922,
>     4.53486, 3.30098, 3.8572, 1.97145, -4.39978, -1.18065, 5.75535,
>     10.227, 9.24193, 14.7518, 16.7049, 2.46144, -23.7603, -6.95984,
>     -12.1827, 10.4526, 0.0706585, 4.84537, 7.81757, 1.99304,
>     -32.6947, -1.00587, 35.229, 34.2314, 30.4428, 22.2066, -17.7357,
>     -32.0899, 34.5392, 33.4394, -1.37745, -6.26124, -0.815708,
>     8.91883, 9.02382, 8.76263, -8.16761, -11.1727, 18.9067, 15.0293,
>     9.97694, 4.92582, 2.9718, 4.79608, 5.26987, 2.84495, -0.264973,
>     0.20777, 3.36723, 4.50213, 4.51221, 2.79895, 6.4508, -0.770261,
>     7.62994, 2.5534, -2.43617, -17.015, 5.25272, -12.8585, -1.89404,
>     24.5016, 24.5592, 21.4044, 11.1924, 7.70434, -4.09892, -4.29682,
>     0.10429, 15.62, 15.2757, 1.12576, 12.3537, 6.28031, 6.28031,
>     6.28031, 9.70625, 9.70625, 16.6939, 16.6939, -16.9003, -16.9003,
>     -16.5469, -16.5469, -1.24881, 2.12382, -8.88365, 11.8552,
>     18.6224, 22.4818, 17.7073, 7.05875, 5.60178, 7.24009, 3.48756,
>     9.56937, 10.7906, 13.3156, 2.31384, -11.7071, -5.06014, 11.9814,
>     9.25461, 10.2528, 1.04765, -3.92472, 0.97033, -6.84208, 7.41494,
>     13.7583, 6.60244, 5.18133, -9.85804, -4.08612, 10.1503, 5.32709,
>     4.55223, -0.413365, -5.7495, 3.18065, -5.70216, -7.24117,
>     -7.31205, 12.0855, 4.33021, -4.98771, -2.93681), integer.Depth = c(5,
>     5, 6, 6, 6, 6, 7, 7, 7, 8, 8, 9, 9, 9, 9, 9, 10, 10, 10,
>     11, 12, 12, 13, 13, 14, 15, 15, 16, 16, 17, 17, 17, 18, 18,
>     18, 19, 19, 19, 19, 20, 20, 20, 21, 21, 22, 22, 23, 23, 23,
>     24, 24, 24, 25, 25, 5, 6, 6, 7, 7, 8, 8, 8, 8, 9, 9, 10,
>     10, 11, 11, 12, 12, 13, 13, 14, 14, 14, 15, 15, 15, 16, 16,
>     17, 17, 18, 18, 18, 19, 19, 20, 20, 21, 22, 22, 23, 23, 24,
>     24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, 5, 6, 6, 6, 6,
>     7, 7, 8, 8, 8, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 13,
>     13, 14, 14, 14, 15, 15, 16, 16, 17, 17, 18, 19, 19, 20, 21,
>     21, 22, 22, 23, 23, 5, 6)), .Names = c("Cruise", "Station",
> "Lon", "Lat", "Depth", "Temperature.oC", "Salinity", "Fluoresence.Volts",
> "Density.kg.m3", "Brunt.Vaisala.Freq.cycl.h", "integer.Depth"
> ), row.names = c("19", "20", "21", "22", "23", "24", "25", "26",
> "27", "28", "29", "30", "31", "32", "33", "34", "35", "36", "37",
> "38", "39", "40", "41", "42", "43", "44", "45", "46", "47", "48",
> "49", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59",
> "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "70",
> "71", "72", "88", "89", "90", "91", "92", "93", "94", "95", "96",
> "97", "98", "99", "100", "101", "102", "103", "104", "105", "106",
> "107", "108", "109", "110", "111", "112", "113", "114", "115",
> "116", "117", "118", "119", "120", "121", "122", "123", "124",
> "125", "126", "127", "128", "129", "130", "131", "132", "133",
> "134", "135", "136", "137", "138", "139", "140", "154", "155",
> "156", "157", "158", "159", "160", "161", "162", "163", "164",
> "165", "166", "167", "168", "169", "170", "171", "172", "173",
> "174", "175", "176", "177", "178", "179", "180", "181", "182",
> "183", "184", "185", "186", "187", "188", "189", "190", "191",
> "192", "193", "194", "209", "210"), class = "data.frame")
>
> When I run this code on the full dataset, calculations continue long enough
> to suggest I am generating a huge matrix, so perhaps I'm doing something
> silly? Eventually (well, after maybe 5 minutes) I get a by class object of
> 109 rows (depth category) by 288 columns (station category), so it does seem
> to be working.
>
> I know that you use sapply to get the by class back to a data.frame. I want
> to extract a matrix of mean densities (one of the original variables) at
> each of the 109 depths and 288 stations.
> I have not quite got this right...can you help?
>
> Thanks in advance
>
> Sam
> ----
> Sam McClatchie,
> Biological oceanography
> South Australian Aquatic Sciences Centre

You might try the summarize function in the Hmisc package.
--
Frank E Harrell Jr   Professor and Chair           School of Medicine
Department of Biostatistics   Vanderbilt University

```