tidyr中的隐式排序:: spread和dplyr :: summarize

Question

我的数据是有序观察,我希望在进行操作时尽可能保持顺序.

得到这个问题的答案,我把"B"放在数据框中的"A"之前.得到的宽数据按"名称"列排序,即首先是"A",然后是"B".

df = data.frame(name=c("B","B","A","A"),
                group=c("g1","g2","g1","g2"),
                V1=c(10,40,20,30),
                V2=c(6,3,1,7))

gather(df, Var, Val, V1:V2) %>% 
unite(VarG, Var, group) %>% 
spread(VarG, Val)

  name V1_g1 V1_g2 V2_g1 V2_g2
1    A    20    30     1     7
2    B    10    40     6     3

有没有办法保持原始订单？像这样:

  name V1_g1 V1_g2 V2_g1 V2_g2
1    B    10    40     6     3
2    A    20    30     1     7

04/02编辑:我刚刚发现了dplyr::summarise排序.arrange(name, df$name)仍然可以恢复订单.但我想知道从包装设计中是否需要额外的分类？

df %>% 
  group_by(name) %>% 
  summarise(n()) %>% 

  name n()
1    A   2
2    B   2

Answer 1

您可以根据原始数据框中的顺序按名称排序:

gather(df, Var, Val, V1:V2) %>% 
  unite(VarG, Var, group) %>% 
  spread(VarG, Val) %>%
  arrange( order(match(name, df$name)))

#   name V1_g1 V1_g2 V2_g1 V2_g2
# 1    B    10    40     6     3
# 2    A    20    30     1     7

Answer 2

订单取自因子水平的顺序.

str(df)
'data.frame':   4 obs. of  4 variables:
 $ name : Factor w/ 2 levels "A","B": 2 2 1 1
 $ group: Factor w/ 2 levels "g1","g2": 1 2 1 2
 $ V1   : num  10 40 20 30
 $ V2   : num  6 3 1 7

看到水平是"A","B".

因此,如果您将级别的顺序设置为它们显示的顺序,它将起作用:

df = data.frame(name=c("B","B","A","A"),
                group=c("g1","g2","g1","g2"),
                V1=c(10,40,20,30),
                V2=c(6,3,1,7))

df %>% 
    mutate(name = factor(name,levels=unique(name))) %>% 
    mutate(group = factor(group,levels=unique(group))) %>% 
    gather(Var, Val, V1:V2) %>% 
    unite(VarG, Var, group) %>% 
    spread(VarG, Val)

结果是:

  name V1_g1 V1_g2 V2_g1 V2_g2
1    B    10    40     6     3
2    A    20    30     1     7