summarise與with plyr的ddply函數一起使用時，默認情況下會刪除空類別。您可以通過添加更改此行為.drop = FALSE。但是，當summarise與結合使用時，這是行不通的dplyr。還有另一種方法可以在結果中保留空類別嗎？這是偽數據的示例。library(dplyr)df = data.frame(a=rep(1:3,4), b=rep(1:2,6))# Now add an extra level to df$b that has no corresponding value in df$adf$b = factor(df$b, levels=1:3)# Summarise with plyr, keeping categories with a count of zeroplyr::ddply(df, "b", summarise, count_a=length(a), .drop=FALSE) b count_a1 1 62 2 63 3 0# Now try it with dplyrdf %.% group_by(b) %.% summarise(count_a=length(a), .drop=FALSE) b count_a .drop1 1 6 FALSE2 2 6 FALSE不完全是我的期望。有沒有dplyr達到同樣的結果的方法.drop=FALSE的plyr？
3 回答
青春有我
TA貢獻1784條經驗 獲得超8個贊
由于dplyr 0.8 group_by獲得了.drop滿足您要求的參數：
df = data.frame(a=rep(1:3,4), b=rep(1:2,6))
df$b = factor(df$b, levels=1:3)
df %>%
group_by(b, .drop=FALSE) %>%
summarise(count_a=length(a))
#> # A tibble: 3 x 2
#> b count_a
#> <fct> <int>
#> 1 1 6
#> 2 2 6
#> 3 3 0
@Moody_Mudskipper的答案還有另一條注釋：.drop=FALSE當一個或多個分組變量未編碼為因素時，使用可能會產生意外結果。請參閱以下示例：
library(dplyr)
data(iris)
# Add an additional level to Species
iris$Species = factor(iris$Species, levels=c(levels(iris$Species), "empty_level"))
# Species is a factor and empty groups are included in the output
iris %>% group_by(Species, .drop=FALSE) %>% tally
#> Species n
#> 1 setosa 50
#> 2 versicolor 50
#> 3 virginica 50
#> 4 empty_level 0
# Add character column
iris$group2 = c(rep(c("A","B"), 50), rep(c("B","C"), each=25))
# Empty groups involving combinations of Species and group2 are not included in output
iris %>% group_by(Species, group2, .drop=FALSE) %>% tally
#> Species group2 n
#> 1 setosa A 25
#> 2 setosa B 25
#> 3 versicolor A 25
#> 4 versicolor B 25
#> 5 virginica B 25
#> 6 virginica C 25
#> 7 empty_level <NA> 0
# Turn group2 into a factor
iris$group2 = factor(iris$group2)
# Now all possible combinations of Species and group2 are included in the output,
# whether present in the data or not
iris %>% group_by(Species, group2, .drop=FALSE) %>% tally
#> Species group2 n
#> 1 setosa A 25
#> 2 setosa B 25
#> 3 setosa C 0
#> 4 versicolor A 25
#> 5 versicolor B 25
#> 6 versicolor C 0
#> 7 virginica A 0
#> 8 virginica B 25
#> 9 virginica C 25
#> 10 empty_level A 0
#> 11 empty_level B 0
#> 12 empty_level C 0
Created on 2019-03-13 by the reprex package (v0.2.1)
MMMHUHU
TA貢獻1834條經驗 獲得超8個贊
這個問題仍然存在，但是與此同時，尤其是因為您的數據已經被考慮到了，您可以使用complete“ tidyr”獲取可能要查找的內容：
library(tidyr)
df %>%
group_by(b) %>%
summarise(count_a=length(a)) %>%
complete(b)
# Source: local data frame [3 x 2]
#
# b count_a
# (fctr) (int)
# 1 1 6
# 2 2 6
# 3 3 NA
如果您希望替換值為零，則需要使用進行指定fill：
df %>%
group_by(b) %>%
summarise(count_a=length(a)) %>%
complete(b, fill = list(count_a = 0))
# Source: local data frame [3 x 2]
#
# b count_a
# (fctr) (dbl)
# 1 1 6
# 2 2 6
# 3 3 0
- 3 回答
- 0 關注
- 967 瀏覽
添加回答
舉報
0/150
提交
取消