r - 将每日数据汇总为几周

Question

我的数据类似于以下结构，其中 when 变量表示测量日期:

## 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

我需要计算一段时间内 y 的平均值。例如，以下计算每日平均值:

## 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

我很难计算每周平均值。这是我到目前为止所尝试过的:

## 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 lubridate 包中的 week 函数会忽略我的数据跨年生成的事实。因此，如果我使用与每日平均值类似的代码，我将汇总属于不同年份(但同一周数)的观察结果。我该如何解决这个问题？

Answer 1

您可以使用 %V (来自 ?strptime )数周，并将其与年份结合起来。

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

“周”有不同的变体，具体取决于您的偏好。

%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.