R 选择按值排序后的顶行数据

我有以下数据：

dat.melt <- structure(list(CellTypes = structure(c(62L, 35L, 73L, 45L, 14L, 
22L, 46L, 13L, 68L, 21L, 1L, 10L, 64L, 24L, 72L, 58L, 51L, 9L, 
60L, 37L, 34L, 49L, 33L, 2L, 50L, 32L, 11L, 52L, 44L, 66L, 8L, 
5L, 47L, 59L, 53L, 7L, 6L, 77L, 75L, 17L, 27L, 61L, 20L, 18L, 
19L, 16L, 54L, 15L, 41L, 3L, 63L, 48L, 57L, 43L, 70L, 40L, 12L, 
76L, 74L, 29L, 28L, 25L, 30L, 42L, 39L, 56L, 4L, 67L, 71L, 31L, 
36L, 23L, 38L, 69L, 55L, 26L, 65L, 62L, 35L, 73L, 45L, 14L, 22L, 
46L, 13L, 68L, 21L, 1L, 10L, 64L, 24L, 72L, 58L, 51L, 9L, 60L, 
37L, 34L, 49L, 33L, 2L, 50L, 32L, 11L, 52L, 44L, 66L, 8L, 5L, 
47L, 59L, 53L, 7L, 6L, 77L, 75L, 17L, 27L, 61L, 20L, 18L, 19L, 
16L, 54L, 15L, 41L, 3L, 63L, 48L, 57L, 43L, 70L, 40L, 12L, 76L, 
74L, 29L, 28L, 25L, 30L, 42L, 39L, 56L, 4L, 67L, 71L, 31L, 36L, 
23L, 38L, 69L, 55L, 26L, 65L), .Label = c("3T3-L1", "Adipose Brown", 
"Adipose White", "Adrenal Gland", "B Cells (GL7 neg; Alum)", 
"B Cells (GL7 neg; KLH)", "B Cells (GL7 pos; Alum)", "B Cells (GL7 pos; KLH)", 
"B Cells Marginal Zone", "B220+ Dend. Cells", "BA/F3", "Bladder", 
"Bone", "Bone Marrow", "C2C12", "CD4+ SP Thymoctyes", "CD4+ T cells", 
"CD4+/CD8+ DP Thymocytes", "CD8+ SP Thymocytes", "CD8+ T cells", 
"CD8a+ Dend. Cells Lymphoid", "CD8a+ Dend. Cells Myeloid", "Ciliary Bodies", 
"Common Myeloid Progenitor", "Cornea", "Dorsal Root Ganglia", 
"Embryonic Fibroblasts", "Embryonic Stem Line Bruce4 P13", "Embryonic Stem Line V26 2 P16", 
"Epidermis", "Eyecup", "Follicular B Cells", "Foxp3+ Tcells", 
"Granulo Monoprogenitor", "Granulocytes", "Heart", "Hematopoietic Stem Cells", 
"Iris", "Kidney", "Lacrimal Gland", "Large Intestine", "Lens", 
"Liver", "Lung", "Lymph Nodes", "Macrophage Peri ", "Mammary Gland", 
"Mammary Gland Non-Lactating", "Mast Cells", "Mast Cells IgE", 
"Mast Cells IgE 1hr", "Mast Cells IgE 6hr", "Megaerythrocyte Progenitor", 
"mIMCD-3 Cells", "MIN6 cells", "Neuro2a Neuroblastoma Cells", 
"NIH 3T3", "NK Cells", "Osteoblast Day14", "Osteoblast Day21", 
"Osteoblast Day5", "Osteoclasts", "Ovary", "Pancreas", "Pituitary", 
"Placenta", "Prostate", "RAW 264.7 Cells", "Retinal Pigment Epithelium", 
"Salivary Gland", "Skeletal Muscle", "Small Intestine", "Spleen", 
"Stem Cells C3H/10T1/2", "Stomach", "Umbilical Cord", "Uterus"
), class = "factor"), variable = structure(c(1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 
2L, 2L, 2L, 2L, 2L, 2L), .Label = c("LPS_IV_SP", "MPL_IV_SP"), class = "factor"), 
    value = c(3.647, 33.629, 17.838, 33.917, 29.66, 31.694, 32.603, 
    24.152, 19.969, 24.012, 40.101, 12.682, 0.323, 12.846, 5.087, 
    11.707, 16.682, 7.71, 22.472, 10.21, 10.109, 12.643, 12.623, 
    1.48, 13.075, 5.042, 12.19, 11.691, 15.24, 17.073, 5.854, 
    5.188, 11.983, 18.679, 6.406, 4.474, 5.445, 8.144, 0.739, 
    3.652, 14.232, 17.1, 2.603, 1.762, 1.993, 3.475, 10.305, 
    7.457, 1.189, 2.895, 4.181, 3.06, 5.885, 3.063, 2.532, 1.662, 
    3.86, 5.094, 5.916, 4.553, 3.703, 2.546, 0.764, 0.597, 1.39, 
    2.933, 0.665, 0.121, 0.257, 0.764, 0.196, 0.208, 0.232, 0.001, 
    0.004, 0.035, 0.036, 56.156, 53.485, 48.206, 45.975, 41.067, 
    40.581, 38.155, 33.009, 29.468, 29.219, 27.945, 19.165, 15.985, 
    15.682, 15.077, 14.72, 13.856, 13.576, 12.914, 12.77, 12.577, 
    12.526, 11.05, 10.532, 10.008, 9.942, 9.238, 8.67, 8.237, 
    7.938, 7.819, 7.55, 7.349, 7.217, 7.146, 6.158, 5.852, 5.368, 
    5.328, 5.126, 4.887, 4.767, 4.24, 3.858, 3.816, 3.676, 3.318, 
    3.118, 2.459, 2.269, 2.266, 2.201, 1.467, 1.418, 1.368, 1.267, 
    1.077, 1.022, 0.835, 0.667, 0.655, 0.609, 0.53, 0.452, 0.24, 
    0.239, 0.211, 0.124, 0.084, 0.05, 0.028, 0.024, 0.016, 0.007, 
    0.006, 0.003, 0.002)), row.names = c(NA, -154L), .Names = c("CellTypes", 
"variable", "value"), class = "data.frame")

对于每个变量MPL_IV_SP和LPS_IV_SP，我希望选择按值降序排列的前5行“单元格类型”。我该怎么做呢？

我们可以使用top\n

注意：在另一个答案中，没有进行排序。但是，我可以理解有偏见的投票。

我们可以使用top\n

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注意：在另一个答案中，没有进行排序。但是，我可以理解有偏见的投票。

您也可以使用data.table包。代码如下：

library(data.table)
dat.melt <- data.table(dat.melt)
dat.melt[, .SD[1:5], by=variable]

---

data.table的优点是它比data.frame快

也可以使用data.table包。代码如下：

library(data.table)
dat.melt <- data.table(dat.melt)
dat.melt[, .SD[1:5], by=variable]

data.table的优点是它比data.frame快

library(data.table)
dat.melt <- data.table(dat.melt)
dat.melt[, .SD[1:5], by=variable]