对因子的排序与子集

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Lore Dirick

Manager of Data Science Curriculum at Flatiron School

设置顺序

ch4_vid2_slides.004.png

rank <- c("low", "medium", "low", "medium", "high")

rank_wrong_order <- ordered(rank)

rank_wrong_order

low    medium low    medium high  
Levels: high < low < medium

rank_order <- factor(rank, ordered = TRUE,
                     levels = c("low", "medium", "high"))
rank_order

low    medium low    medium high  
Levels: low < medium < high

summary(rank_order)

low medium   high 
  2      2      1

# 仅 low
rank_order[c(1,3)]

low low
Levels: low < medium < high

summary(rank_order[c(1,3)])

low medium   high 
  2      0      0

# 仅 low，删除 medium 与 high 的水平
rank_order[c(1,3), drop = TRUE]

low low
Levels: low

summary(rank_order[c(1,3), drop = TRUE])

low 
  2

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