根据数据中水平出现的顺序对因子水平进行排序。

Question

这是我使用readHTMLtable从互联网加载的数据框的一部分：

head(tt,59)
    year         sport                      event      athlete_id  medal
1   1896 Track & Field                   100m Men      BURKETOM01   GOLD
2   1896 Track & Field                   100m Men      HOFMAFRI01 SILVER
3   1896 Track & Field                   100m Men       LANEFRA01 BRONZE
4   1896 Track & Field                   100m Men      SZOKOALA01 BRONZE
5   1896 Track & Field                   400m Men      BURKETOM01   GOLD
6   1896 Track & Field                   400m Men      JAMISHER01 SILVER
7   1896 Track & Field                   400m Men      GMELICHA01 BRONZE
8   1896 Track & Field                   800m Men      FLACKTED01   GOLD
9   1896 Track & Field                   800m Men D<C1>NIN<C1>N01 SILVER
10  1896 Track & Field                   800m Men      GOLEMDEM01 BRONZE
11  1896 Track & Field                  1500m Men      FLACKTED01   GOLD
12  1896 Track & Field                  1500m Men      BLAKEART01 SILVER
13  1896 Track & Field                  1500m Men      LERMUALB01 BRONZE
14  1896 Track & Field               Marathon Men      LOUISSPI01   GOLD
15  1896 Track & Field               Marathon Men      VASILCHA01 SILVER
16  1896 Track & Field               Marathon Men      KELLNGYU01 BRONZE
17  1896 Track & Field           110m Hurdles Men      CURTITOM01   GOLD
18  1896 Track & Field           110m Hurdles Men      GOULDGRA01 SILVER
19  1896 Track & Field              High Jump Men      CLARKELL01   GOLD
20  1896 Track & Field              High Jump Men      CONNOJAM01 SILVER
21  1896 Track & Field              High Jump Men      GARREBOB01 SILVER
22  1896 Track & Field             Pole Vault Men       HOYTBIL01   GOLD
23  1896 Track & Field             Pole Vault Men      TYLERALB01 SILVER
24  1896 Track & Field             Pole Vault Men      THEODIOA01 BRONZE
25  1896 Track & Field             Pole Vault Men      DAMASEVA01 BRONZE
26  1896 Track & Field              Long Jump Men      CLARKELL01   GOLD
27  1896 Track & Field              Long Jump Men      GARREBOB01 SILVER
28  1896 Track & Field              Long Jump Men      CONNOJAM01 BRONZE
29  1896 Track & Field            Triple Jump Men      CONNOJAM01   GOLD
30  1896 Track & Field            Triple Jump Men   TUFF<C8>ALE01 SILVER
31  1896 Track & Field            Triple Jump Men      PERSAIOA01 BRONZE
32  1896 Track & Field               Shot Put Men      GARREBOB01   GOLD
33  1896 Track & Field               Shot Put Men      GOUSKMIL01 SILVER
34  1896 Track & Field               Shot Put Men      PAPASGEO01 BRONZE
35  1896 Track & Field           Discus Throw Men      GARREBOB01   GOLD
36  1896 Track & Field           Discus Throw Men      PARASPAN01 SILVER
37  1896 Track & Field           Discus Throw Men      VERSISOT01 BRONZE
38  1896       Cycling 2000m Sprint (Scratch) Men      MASSOPAU01   GOLD
39  1896       Cycling 2000m Sprint (Scratch) Men      NIKOLSTA01 SILVER
40  1896       Cycling 2000m Sprint (Scratch) Men   FLAMEL<C9>O01 BRONZE
41  1896       Cycling   Individual Road Race Men      KONSTARI01   GOLD
42  1896       Cycling   Individual Road Race Men      GOEDRAUG01 SILVER
43  1896       Cycling   Individual Road Race Men      BATTEEDW01 BRONZE
44  1896       Cycling               One-Lap Race      MASSOPAU01   GOLD
45  1896       Cycling               One-Lap Race      NIKOLSTA01 SILVER
46  1896       Cycling               One-Lap Race      SCHMAADO01 BRONZE
47  1896       Cycling            10km Track Race      MASSOPAU01   GOLD
48  1896       Cycling            10km Track Race   FLAMEL<C9>O01 SILVER
49  1896       Cycling            10km Track Race      SCHMAADO01 BRONZE
50  1896       Cycling           100km Track Race   FLAMEL<C9>O01   GOLD
51  1896       Cycling           100km Track Race      KOLETGEO01 SILVER
52  1896       Cycling               12-Hour Race      SCHMAADO01   GOLD
53  1896       Cycling               12-Hour Race      KEEPIFRA01 SILVER
54  1896       Fencing           Foil, Individual      GRAVEEUG01   GOLD
55  1896       Fencing           Foil, Individual      CALLOHEN01 SILVER
56  1896       Fencing           Foil, Individual      PIERRPER01 BRONZE
57  1896       Fencing          Sabre, Individual      GEORGIOA01   GOLD
58  1896       Fencing          Sabre, Individual      KARAKTEL01 SILVER
59  1896       Fencing          Sabre, Individual      NIELSHOL01 BRONZE

正如你所看到的，变量sport是一个因子。当我检查水平时，得到以下结果：

levels(tt$sport)
[1] "Cycling"       "Fencing"       "Gymnastics"    "Shooting"      "Swimming"      "Tennis" 
[7] "Track & Field" "Weightlifting" "Wrestling 

由于某些原因，级别显示的顺序与数据框中的顺序不匹配。我正在寻找一种使用levels函数的方法，它将按照第一次出现的顺序组织级别列表，类似于以下内容：

levels(medals.df$tt)
[1] "Track & Field" "Cycling"       "Fencing"       "Gymnastics"    "Shooting"    "Swimming"
[7] "Tennis"        "Weightlifting" "Wrestling"

需要记住的另一件事是，列“sport”不是“块设计”，这意味着前59行具有相邻的相同值，但在整个数据框中并非如此。

- Lee

Answer 1

我使用了@gung在他的回答中设置的数据框：

d <- read.table(text="rn    year    sport          event      athlete_id medal
1   1896 'Track & Field'                   '100m Men'      'BURKETOM01'   'GOLD'
53  1896       'Cycling'               '12-Hour Race'      'KEEPIFRA01' 'SILVER'
54  1896       'Fencing'           'Foil, Individual'      'GRAVEEUG01'   'GOLD'
55  1896       'Gymnastics'           'Foil, Individual'      'CALLOHEN01' 'SILVER'
56  1896       'Shooting'           'Foil, Individual'      'PIERRPER01' 'BRONZE'
57  1896       'Swimming'          'Sabre, Individual'      'GEORGIOA01'   'GOLD'
58  1896       'Tennis'          'Sabre, Individual'      'KARAKTEL01' 'SILVER'
58  1896       'Weightlifting'          'Sabre, Individual'      'KARAKTEL01' 'SILVER'
59  1896       'Wrestling'          'Sabre, Individual'      'NIELSHOL01' 'BRONZE'", 
            header=T)

levels(d$sport)

然后，您可以像这样在因子函数中使用unique(d$sport)：

d$sport <- factor(d$sport, levels=unique(d$sport))
# Check the results:
levels(d$sport)

- KenHBS

Answer 2

请注意，我必须调整您的数据集，以便列出您列出的所有级别，并按您指定的顺序进行排序。从那里，我编写了一个简单的函数，按照数据集中它们出现的顺序输出这些级别。关键是使用which（列出匹配标准的观测行号）、min（选择最低值）和order（告诉您从最低到最高使用的顺序）。

d <- read.table(text="rn    year    sport          event      athlete_id  medal
1   1896 'Track & Field'                   '100m Men'      'BURKETOM01'   'GOLD'
53  1896       'Cycling'               '12-Hour Race'      'KEEPIFRA01' 'SILVER'
54  1896       'Fencing'           'Foil, Individual'      'GRAVEEUG01'   'GOLD'
55  1896       'Gymnastics'           'Foil, Individual'      'CALLOHEN01' 'SILVER'
56  1896       'Shooting'           'Foil, Individual'      'PIERRPER01' 'BRONZE'
57  1896       'Swimming'          'Sabre, Individual'      'GEORGIOA01'   'GOLD'
58  1896       'Tennis'          'Sabre, Individual'      'KARAKTEL01' 'SILVER'
58  1896       'Weightlifting'          'Sabre, Individual'      'KARAKTEL01' 'SILVER'
59  1896       'Wrestling'          'Sabre, Individual'      'NIELSHOL01' 'BRONZE'", 
                header=T)

levels(d$sport)
# [1] "Cycling"       "Fencing"       "Gymnastics"    "Shooting"     
# [5] "Swimming"      "Tennis"        "Track & Field" "Weightlifting"
# [9] "Wrestling"    

level.order <- function(var){
  l <- levels(var)
  o <- c()
  for(i in 1:length(l)){
    o[i] <- min(which(var==l[i]))
  }
  return(l[order(o)])
}
level.order(d$sport)
# [1] "Track & Field" "Cycling"       "Fencing"       "Gymnastics"   
# [5] "Shooting"      "Swimming"      "Tennis"        "Weightlifting"
# [9] "Wrestling"    

如果你想改变默认排序（按字母顺序）为数据集中显示的级别顺序，你可以使用factor。请考虑以下内容：

levels(d$sport)
# [1] "Cycling"       "Fencing"       "Gymnastics"    "Shooting"     
# [5] "Swimming"      "Tennis"        "Track & Field" "Weightlifting"
# [9] "Wrestling"    
d$sport <- factor(d$sport, levels=level.order(d$sport))
levels(d$sport)
# [1] "Track & Field" "Cycling"       "Fencing"       "Gymnastics"   
# [5] "Shooting"      "Swimming"      "Tennis"        "Weightlifting"
# [9] "Wrestling"    

- gung - Reinstate Monica

---

你可以使用d$sport <- factor(d$sport, levels = unique(d$sport))来替代level.order()函数。 - KenHBS

不错的观点，@KenS。我不知道unique()总是按它们出现的顺序列出值。为什么不把它作为正式答案呢？ - gung - Reinstate Monica

不客气，@Lee。如果KenS.使用unique发布了答案，你应该把勾选标记移到他那里。那将是一个比我提供的更简单、更优雅的解决方案。 - gung - Reinstate Monica

@Lee，当然这是你的决定，但你可能想考虑将勾选标记切换到KenS的答案上，那是比我的更干净的解决方案。 - gung - Reinstate Monica