將每日資料匯總為數周

我有類似于以下結構的資料，其中when變數表示測量日期：

## Generate data.
set.seed(1986)

n <- 1000
y <- rnorm(n)

when <- as.POSIXct(strftime(seq(as.POSIXct("2021-11-01 23:00:00 UTC", tryFormats = "%Y-%m-%d"), 
                 as.POSIXct("2022-11-01 23:00:00 UTC", tryFormats = "%Y-%m-%d"), 
                 length.out = n), format = "%Y-%m-%d"))

dta <- data.frame(y, when)
head(dta)
#>             y       when
#> 1 -0.04625141 2021-11-01
#> 2  0.28000082 2021-11-01
#> 3  0.25317063 2021-11-01
#> 4 -0.96411077 2021-11-02
#> 5  0.49222664 2021-11-02
#> 6 -0.69874551 2021-11-02

我需要計算y一段時間內的平均值。例如，以下計算每日平均值：

## Compute daily averages of y.
library(dplyr)

daily_avg <- dta %>% 
  group_by(when) %>%
  summarise(daily_mean = mean(y)) %>% 
  ungroup()

daily_avg
#> # A tibble: 366 × 2
#>    when                daily_mean
#>    <dttm>                   <dbl>
#>  1 2021-11-01 00:00:00     0.162 
#>  2 2021-11-02 00:00:00    -0.390 
#>  3 2021-11-03 00:00:00    -0.485 
#>  4 2021-11-04 00:00:00    -0.152 
#>  5 2021-11-05 00:00:00     0.425 
#>  6 2021-11-06 00:00:00     0.726 
#>  7 2021-11-07 00:00:00     0.855 
#>  8 2021-11-08 00:00:00     0.0608
#>  9 2021-11-09 00:00:00    -0.995 
#> 10 2021-11-10 00:00:00     0.395 
#> # … with 356 more rows

我很難計算每周平均值。這是我到目前為止所嘗試的：

## Fail - compute weekly averages of y.
library(lubridate)

dta$week <- week(dta$when) # This is wrong.
dta[165: 171, ]
#>              y       when week
#> 165  0.9758333 2021-12-30   52
#> 166 -0.8630091 2021-12-31   53
#> 167  0.3054031 2021-12-31   53
#> 168  1.2814421 2022-01-01    1
#> 169  0.1025440 2022-01-01    1
#> 170  1.3665411 2022-01-01    1
#> 171 -0.5373058 2022-01-02    1

使用包中的week函式lubridate忽略了我的資料產生多年的事實。因此，如果我使用類似于我用于每日平均值的代碼，我將匯總屬于不同年份的觀察結果（但屬于同一周數）。我該如何解決這個問題？

uj5u.com熱心網友回復：

您可以使用%V(from ?strptime) 數周，并將其與年份結合使用。

dta %>%
  group_by(week = format(when, format = "%Y-%V")) %>%
  summarize(daily_mean = mean(y)) %>%
  ungroup()
# # A tibble: 54 x 2
#    week    daily_mean
#    <chr>        <dbl>
#  1 2021-44     0.179 
#  2 2021-45     0.0477
#  3 2021-46     0.0340
#  4 2021-47     0.356 
#  5 2021-48     0.0544
#  6 2021-49    -0.0948
#  7 2021-50    -0.0419
#  8 2021-51     0.209 
#  9 2021-52     0.251 
# 10 2022-01    -0.197 
# # ... with 44 more rows

根據您的喜好，“周”有不同的變體。

%V
    Week of the year as decimal number (01–53) as defined in ISO 8601.
 If the week (starting on Monday) containing 1 January has four or more
 days in the new year, then it is considered week 1. Otherwise, it is
 the last week of the previous year, and the next week is week 1.
 (Accepted but ignored on input.)

%W
    Week of the year as decimal number (00–53) using Monday as the first
 day of week (and typically with the first Monday of the year as day 1
 of week 1). The UK convention.

uj5u.com熱心網友回復：

您可以從日期和分組中提取年份和星期：

dta %>% 
  mutate(year = year(when),
         week = week(when)) %>%
  group_by(year, week) %>%
  summarise(y_mean = mean(y)) %>%
  ungroup()

#  # A tibble: 54 x 3
#  # Groups:   year, week [54]
#     year  week  y_mean
#    <dbl> <dbl>   <dbl>
#  1  2021    44 -0.222 
#  2  2021    45  0.234 
#  3  2021    46  0.0953
#  4  2021    47  0.206 
#  5  2021    48  0.192 
#  6  2021    49 -0.0831
#  7  2021    50  0.0282
#  8  2021    51  0.196 
#  9  2021    52  0.132 
# 10  2021    53 -0.279 
#  # ... with 44 more rows

標籤：r时间总计的

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