範囲制約

Rでのデータクリーニング

Maggie Matsui

Content Developer @ DataCamp

範囲外の値とは？

SATスコア: 400〜1600
荷物の重さ: 0 lb/kg 以上
成人の心拍数: 60〜100 拍/分

範囲外の値を見つける

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
...

範囲外の値を見つける

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

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

コードで生成した3ビンのヒストグラム。低すぎる箱に1件、範囲内に6件、高すぎる箱に2件。

範囲外の値を見つける

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

範囲外の値の扱い方

行を削除する
欠損値（NA）として扱う
範囲の端で置換する
ドメイン/データの知識に基づく他の値で置換する

行の削除

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)))

コードで生成したヒストグラム。範囲内が6件、下限未満と上限超えは0件。

欠損として扱う

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
...

範囲外の値を置換

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
...

日付の範囲制約

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

範囲外の日付を削除

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

library(assertive)
assert_all_are_in_past(movies$date_recorded)

覚えておきましょう。出力なし = 合格です！

練習しましょう！

Rでのデータクリーニング