如何从 R 中具有日期列条件的不同列获取最大值和平均值？

Question

我正在尝试获取每种污染物的每日平均值和最大值。对每个监测站计算每项污染物的日均值和最大值。

这是我的数据框示例：

df <- data.frame (Station  = c(1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 10),
                  Date = c("31/12/2018", "31/12/2018", "30/12/2018", "1/12/2018", "4/3/2018", "16/3/2018", "16/3/2018", "5/2/2018", "31/12/2018", "6/2/2018", "6/2/2018", "4/3/2018"),
                  NO2 = c(40,55,52,58,76,98,12,14,23,54,53,76),
                  O3 = c(13,12,45,87,72,54,88,102,63,52,64,53))

这是预期的数据帧：

df2 <- data.frame (Station  = c(1, 1, 2, 2, 2, 3, 3, 3, 4, 10),
                    Date = c("31/12/2018",  "30/12/2018", "1/12/2018", "4/3/2018", "16/3/2018", "16/3/2018", "5/2/2018", "31/12/2018", "6/2/2018", "4/3/2018"),
                    MAX_NO2 = c(55,52,58,76,98,12,14,23,54,76),
                    MEAN_NO2 = c(47.5,52,58,76,98,12,14,23,53.5,76),
                    MAX_O3 = c(13,45,87,72,54,88,102,63,64,53),
                    MEAN_O3 = c(12.5,45,87,72,54,88,102,63,58,53))

这是我在中找到的代码。我试过了，但发生错误：

library(dplyr)

df %>%
group_by(Station,Date) %>%
mutate(max.O3 = max(O3), max.NO2 = max(NO2)) %>%
ungroup() %>%
mutate(max.O3 = case_when(O3 == max.O3 ~ max.O3, TRUE ~ NA_real_), max.NO2 = case_when(NO2 == max.NO2 ~ max.NO2, TRUE ~ NA_real_)) %>%
filter(!is.na(max.O3) | !is.na(max.NO2)) %>%
select(-O3,-NO2)

如何获得所需的输出？我首先想到使用 for 循环来迭代值，但我不知道这样做是否正确。类似于：

for i in df$Station{
   for date in df$date{
      Max_NO2 = max(a)
      Mean_NO2 = mean(a)
      ...
   }
}

Answer 1

我们可以先转换为日期格式，然后我们可以 summarise across 2 列来获取每个组和列的平均值和最大值。然后，我们可以使用 .names 参数来定义列名。

library(tidyverse)
    
df %>%
  mutate(Date = as.Date(Date, "%d/%m/%Y")) %>% 
  group_by(Station, Date) %>%
  summarise(across(NO2:O3, list(MAX = max, MEAN = mean), .names = "{.fn}_{.col}")) %>% 
  ungroup

输出

   Station Date       MAX_NO2 MEAN_NO2 MAX_O3 MEAN_O3
     <dbl> <date>       <dbl>    <dbl>  <dbl>   <dbl>
 1       1 2018-12-30      52     52       45    45  
 2       1 2018-12-31      55     47.5     13    12.5
 3       2 2018-03-04      76     76       72    72  
 4       2 2018-03-16      98     98       54    54  
 5       2 2018-12-01      58     58       87    87  
 6       3 2018-02-05      14     14      102   102  
 7       3 2018-03-16      12     12       88    88  
 8       3 2018-12-31      23     23       63    63  
 9       4 2018-02-06      54     53.5     64    58  
10      10 2018-03-04      76     76       53    53

如何从 R 中具有日期列条件的不同列获取最大值和平均值？

How do obtain max and mean values from different columns with a Date column condition in R?

for-loop

r

date

dataframe