使用 for 循环为数据框动态生成子集列名称

Question

对于以下数据帧 df：

df <- structure(list(id = c("M0000607", "M0000609", "M0000612"), `2021-08(actual)` = c(12.6, 
19.2, 8.3), `2021-09(actual)` = c(10.3, 17.3, 6.4), `2021-10(actual)` = c(8.9, 
15.7, 5.3), `2021-11(actual)` = c(7.3, 14.8, 3.1), `2021-12(actual)` = c(6.1, 
14.2, 3.5), `2021-08(pred)` = c(11.65443222, 14.31674997, 7.084180415
), `2021-09(pred)` = c(12.29810914, 17.7143733, 6.057927385), 
    `2021-10(pred)` = c(9.619846116, 15.54553601, 6.525992602
    ), `2021-11(pred)` = c(8.352097939, 13.97318204, 3.164682627
    ), `2021-12(pred)` = c(6.113631596, 14.16243166, 3.288372517
    ), `2021-08(error)` = c(2.082307066, 1.146759554, 0.687406723
    ), `2021-09(error)` = c(1.631350383, 2.753457736, 2.952737781
    ), `2021-10(error)` = c(0.945567783, 4.883250027, 1.215819585
    ), `2021-11(error)` = c(1.998109138, 0.414373304, 0.342072615
    ), `2021-12(error)` = c(0.719846116, 0.154463985, 1.225992602
    )), class = "data.frame", row.names = c(NA, -3L))

假设我的最终 objective 是将绘图函数重复应用于 df 的子集：

plot_fun <- function(...)
  ggplot()

更具体地说，我将循环 year_months <- c('2021-12', '2021-11', '2021-10') 的每个元素并应用 plot_fun，因此首先，我需要为 year_months 的每个元素对选定列进行子集化。

逻辑是：对于特定的年月，我会选择：id，最近三个月的实际值，最近一个月的误差和预测值。例如，对于 year_month '2021-12', '2021-11', '2021-10'，子集列为：

2021-12: selected_cols <- c('id', "2021-10(actual)", "2021-11(actual)", "2021-12(actual)",
                            "2021-12(pred)", "2021-12(error)")

2021-11: selected_cols <- c('id', "2021-09(actual)", "2021-10(actual)", "2021-11(actual)",
                            "2021-11(pred)", "2021-11(error)")

2021-10: selected_cols <- c('id', "2021-08(actual)", "2021-09(actual)", "2021-10(actual)",
                            "2021-12(pred)", "2021-12(error)")

最后，我将运行代码（伪）如下：

for year_month in year_months{
  selected_cols <- ...
  plot_fun(selected_cols)
}

现在我的问题是如何编写一个 for 循环函数来为每个选定的 year_month 生成列名向量？

我的试用代码（还不简洁）为2021-12生成列：

date_pre_n_months <- function(end_date, x) {
  floor_date(as.Date(end_date) - months(x), 'month')  
}

end_date <- '2021-12-31'
begin_date <- date_pre_n_months(end_date, 3)

year_month <- seq(as.Date("2021-10-31"), as.Date("2021-12-31"), by = "month")
act <- paste0(strftime(year_month, format="%Y-%m"), '(actual)')
pred <- paste0(strftime(end_date, format="%Y-%m"), '(pred)')
error <- paste0(strftime(end_date, format="%Y-%m"), '(error)')

selected_cols <- c('id', act, pred, error)
selected_cols

输出：

"id"              "2021-10(actual)" "2021-12(actual)" "2021-12(actual)" "2021-12(pred)"   "2021-12(error)"

Answer 1

在 lubridate 包的帮助下，您可以像这样在 base R 中完成它。

year_months <- c('2021-12', '2021-11', '2021-10')  
curr <- lubridate::ym(year_months)
prev <- curr - months(2L)
mapply(function(x, y) {
  df[c(
    "id", 
    format(seq.Date(y, x, by = "month"), "%Y-%m(actual)"), 
    format(x, "%Y-%m(pred)"), 
    format(x, "%Y-%m(error)")
  )]
}, curr, prev, SIMPLIFY = FALSE)

输出

[[1]]
        id 2021-10(actual) 2021-11(actual) 2021-12(actual) 2021-12(pred) 2021-12(error)
1 M0000607             8.9             7.3             6.1      6.113632      0.7198461
2 M0000609            15.7            14.8            14.2     14.162432      0.1544640
3 M0000612             5.3             3.1             3.5      3.288373      1.2259926

[[2]]
        id 2021-09(actual) 2021-10(actual) 2021-11(actual) 2021-11(pred) 2021-11(error)
1 M0000607            10.3             8.9             7.3      8.352098      1.9981091
2 M0000609            17.3            15.7            14.8     13.973182      0.4143733
3 M0000612             6.4             5.3             3.1      3.164683      0.3420726

[[3]]
        id 2021-08(actual) 2021-09(actual) 2021-10(actual) 2021-10(pred) 2021-10(error)
1 M0000607            12.6            10.3             8.9      9.619846      0.9455678
2 M0000609            19.2            17.3            15.7     15.545536      4.8832500
3 M0000612             8.3             6.4             5.3      6.525993      1.2158196

如果要将绘图函数应用于 selected 数据框，则

year_months <- c('2021-12', '2021-11', '2021-10')  
curr <- lubridate::ym(year_months)
prev <- curr - months(2L)
plots <- mapply(function(x, y) {
  plot_fun(df[c(
    "id", 
    format(seq.Date(y, x, by = "month"), "%Y-%m(actual)"), 
    format(x, "%Y-%m(pred)"), 
    format(x, "%Y-%m(error)")
  )])
}, curr, prev, SIMPLIFY = FALSE)

为您提供 (gg) 图列表。

更新（也 select 当前月份的去年）。但是，您需要确保数据框中存在您想要 select 的列；否则，你会得到一个错误。

year_months <- c('2021-12', '2021-11', '2021-10')  
curr <- lubridate::ym(year_months)
prev <- curr - months(2L)
mapply(function(x, y) {
  df[c(
    "id", 
    format(c(x - lubridate::years(1L), seq.Date(y, x, by = "month")), "%Y-%m(actual)"),  
    format(x, "%Y-%m(pred)"), 
    format(x, "%Y-%m(error)")
  )]
}, curr, prev, SIMPLIFY = FALSE)

使用 for 循环为数据框动态生成子集列名称

Dynamically generate subset column names for a dataframe using for loop

r

vector

dplyr

stringi