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雷达卡
《R语言实战》书中代码清单7-15如下：
> table2flat<-function(mytable) {
+ df <- as.data.frame(mytable)
+ rows <- dim(df)[1]
+ cols <- dim(df)[2]
+ x <- NULL
+ for (i in 1:rows){
+ for (j in 1:df$Freq[i]){
+ row <- df[i,c(1:(cols-1))]
+ x <- rbind(x,row)
+ }
+ }
+ row.names(x)<-c(1:dim(x)[1])
+ return(x)
+ }
treatment <- rep(c("Placebo", "Treated"), times=3)
improved <- rep(c("None", "Some", "Marked"), each=2)
Freq <- c(29,13,7,17,7,21)
mytable <- as.data.frame(cbind(treatment, improved, Freq))
mytable
table2flat(mytable)
mytable
--------------------------------------------------------------
以下是输出结果：
> mytable
treatment improved Freq
1 Placebo None 29
2 Treated None 13
3 Placebo Some 7
4 Treated Some 17
5 Placebo Marked 7
6 Treated Marked 21
> table2flat(mytable)
treatment improved
1 Placebo None
2 Placebo None
3 Placebo None
4 Placebo None
5 Treated None
6 Placebo Some
7 Placebo Some
8 Placebo Some
9 Placebo Some
10 Placebo Some
11 Treated Some
12 Treated Some
13 Placebo Marked
14 Placebo Marked
15 Placebo Marked
16 Placebo Marked
17 Placebo Marked
18 Treated Marked
19 Treated Marked
20 Treated Marked
> mytable
treatment improved Freq
1 Placebo None 29
2 Treated None 13
3 Placebo Some 7
4 Treated Some 17
5 Placebo Marked 7
6 Treated Marked 21
问题：table2flat(mytable)的结果应该是94条记录，为什么执行结果是20条记录？
由此可以看出：以上书中代码7-15是错误的，把for (j in 1:df$Freq[i])改成 for (j in 1:as.integer(as.character((df$Freq[i]))))就可以了。
这里有一个细节，需要理解R中factor类型，factor类型在R内部存储时候是level值（整数），level值的factor类型直接转化成numeric或者integer都将导致错误把level值（整数）转出数值，与想要的结果不符，应该是先转成character再转成integer。
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