範圍限制

R 的資料清理

Maggie Matsui

Content Developer @ DataCamp

什麼是超出範圍的值？

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找出超出範圍的值

movies

  title                 avg_rating
  <chr>                      <dbl>
1 A Beautiful Mind             4.1
2 La Vita e Bella              4.3
3 Amelie                       4.2
4 Meet the Parents             3.5
5 Unbreakable                  5.8
6 Gone in Sixty Seconds        3.3
...

找出超出範圍的值

breaks <- c(min(movies$avg_rating), 0, 5, max(movies$avg_rating))

ggplot(movies, aes(avg_rating)) +
    geom_histogram(breaks = breaks)

由程式碼產生的三欄長條圖：一筆過低、六筆在範圍內、兩筆過高。

找出超出範圍的值

library(assertive)
assert_all_are_in_closed_range(movies$avg_rating, lower = 0, upper = 5)

Error: is_in_closed_range : movies$avg_rating are not all in the range [0,5].
There were 3 failures:
  Position Value    Cause
1        5   5.8 too high
2        8   6.2 too high
3        9  -4.4  too low

處理超出範圍的值

刪除列
視為遺漏值（NA）
以範圍邊界替換
依領域知識與/或資料集知識改填其他值

刪除列

movies %>%
  filter(avg_rating >= 0, avg_rating <= 5) %>%


  ggplot(aes(avg_rating)) +
  geom_histogram(breaks = c(min(movies$avg_rating), 0, 5, max(movies$avg_rating)))

由程式碼產生的長條圖：6 筆在範圍內，範圍外（低於或高於）為 0。

視為遺漏值

movies

  title                 avg_rating
  <chr>                      <dbl>
1 A Beautiful Mind             4.1
2 La Vita e Bella              4.3
3 Amelie                       4.2
4 Meet the Parents             3.5
5 Unbreakable                  5.8
6 Gone in Sixty Seconds        3.3
...

replace(col, condition, replacement)

movies %>%
  mutate(rating_miss = 
    replace(avg_rating, avg_rating > 5, NA))

  title                rating_miss
  <chr>                      <dbl>
1 A Beautiful Mind             4.1
2 La Vita e Bella              4.3
3 Amelie                       4.2
4 Meet the Parents             3.5
5 Unbreakable                   NA
6 Gone in Sixty Seconds        3.3
...

替換超出範圍的值

movies %>%
  mutate(rating_const = 
           replace(avg_rating, avg_rating > 5, 5))

  title               rating_const
  <chr>                      <dbl>
1 A Beautiful Mind             4.1
2 La Vita e Bella              4.3
3 Amelie                       4.2
4 Meet the Parents             3.5
5 Unbreakable                  5.0
6 Gone in Sixty Seconds        3.3
...

日期範圍限制

assert_all_are_in_past(movies$date_recorded)

Error: is_in_past : movies$date_recorded are not all in the past.
There was 1 failure:
  Position               Value     Cause
1        3 2064-09-22 20:00:00 in future

library(lubridate)
movies %>%
  filter(date_recorded > today())

    title  avg_rating  date_recorded
1  Amelie         4.2  2064-09-23

移除超出範圍的日期

library(lubridate)
movies <- movies %>%
  filter(date_recorded <= today())

library(assertive)
assert_all_are_in_past(movies$date_recorded)

記住，沒有輸出 = 測試通過！

一起來練習吧！

R 的資料清理