如何根據其他類別對因素水平進行排序？

Question

說我有一個有兩個因素的數據框在那裏，我想排序由第二類分組的一個因素的水平。

name <- letters[1:8] 
category <- factor(sample(1:2, 8, replace=T), labels=c("A", "B")) 
my.df <- data.frame(name=name, category=category) 

所以數據幀類似於：

name category 
1 a  A 
2 b  A 
3 c  B 
4 d  B 
5 e  B 
6 f  A 
7 g  A 
8 h  A 

和levels(my.df$name)輸出爲：

[1] "a" "b" "c" "d" "e" "f" "g" "h" 

假設在name的水平總是對應於相同的電平在category在我的數據中，我怎樣才能對名稱的級別進行相應的排序？

Answer 1

這是你想要的嗎？

> levels(my.df$name) <- as.character(unique(my.df[order(my.df$category),]$name)) 
> levels(my.df$name) 
[1] "b" "c" "e" "f" "a" "d" "g" "h" 

Answer 2

我認爲這可能比任何解決方案的更乾淨爲止：

my.df <- 
structure(list(name = structure(1:8, .Label = c("a", "b", "c", 
"d", "e", "f", "g", "h"), class = "factor"), category = structure(c(1L, 
1L, 2L, 2L, 2L, 1L, 1L, 1L), .Label = c("A", "B"), class = "factor")), .Names = c("name", 
"category"), class = "data.frame", row.names = c("1", "2", "3", 
"4", "5", "6", "7", "8")) 

with(my.df, name[order(category)]) 
[1] b d e h a c f g 
Levels: a b c d e f g h 

如果你想relevel因素，可以做的很好，但它並不清楚你希望這種改變是永久的。