我正在尝试根据 2 列有条件地提取唯一值的数量。我想要做的是在考虑“变量”和“日期”时保存唯一观察的长度，并将每个唯一观察保存为列表，以便我可以通过循环运行每个观察。下面是数据框的一个子集和我一直在运行的代码。ncurves 和 ids 中都应该有 9 个独特的观察结果。我在 ncurves 中得到 2 个，ids 保存为数据帧，而不是像我想要的那样通过循环运行的列表。
a <- structure(list(LightIntensity = c(0L, 112L, 0L, 112L, 0L, 112L, 0L, 112L, 0L, 112L, 0L,
112L, 0L, 112L, 0L, 112L, 0L, 112L), variable = c(221L, 221L, 244L, 244L, 12L, 12L, 221L,
221L, 244L, 244L, 12L, 12L, 221L, 221L, 12L, 12L, 244L, 244L), value = c(-1.21625718690742,
0.192572605693232, -1.21625718690742, 0.226570039268424, -0.437571128774482,
0.167029555798728, -0.344666861319387, -0.099033581577414, -0.341605586260893,
0.158985219436985, -0.0728378731631007, 0.108468868197142, -0.227259158534414,
-0.121668829961881, -0.504828403085384, 0.37919920958843, -0.674980508632225,
0.215847519075345), Species = structure(c(1L, 1L, 2L, 2L, 1L, 1L, 1L, 1L, 2L, 2L, 1L, 1L, 1L,
1L, 1L, 1L, 2L, 2L), .Label = c("Montipora capitata", "Porites compressa"), class =
"factor"), Bleach = structure(c(1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 2L,
2L, 2L, 2L), .Label = c("Bleach", "Non-bleach"), class = "factor"), Date = structure(c(1L,
1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("2019-09-16",
"2019-10-02", "2019-10-16"), class = "factor")), row.names = c(1L,
2L, 28L, 29L, 181L, 182L, 361L, 362L, 481L, 482L, 541L, 542L, 761L, 762L, 891L, 892L, 921L,
922L), class = "data.frame")
n <- length(unique(a[c("variable", "Date")]))
ids <- unique(a[c("variable", "Date")])
要提取 data.frame 中的唯一组合，您可以执行以下操作：
a[!duplicated(a[c("variable", "Date")]),]
LightIntensity variable value Species Bleach Date
1 0 221 -1.21625719 Montipora capitata Bleach 2019-09-16
28 0 244 -1.21625719 Porites compressa Non-bleach 2019-09-16
181 0 12 -0.43757113 Montipora capitata Non-bleach 2019-09-16
361 0 221 -0.34466686 Montipora capitata Bleach 2019-10-02
481 0 244 -0.34160559 Porites compressa Non-bleach 2019-10-02
541 0 12 -0.07283787 Montipora capitata Non-bleach 2019-10-02
761 0 221 -0.22725916 Montipora capitata Bleach 2019-10-16
891 0 12 -0.50482840 Montipora capitata Non-bleach 2019-10-16
921 0 244 -0.67498051 Porites compressa Non-bleach 2019-10-16
要获取索引，您可以执行以下操作：
(ids <- which(!duplicated(a[c("variable", "Date")])))
[1] 1 3 5 7 9 11 13 15 17
length(ids)
[1] 9
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