read.xlsx和colClasses

Question

有谁知道为什么参数colClasses似乎不适用于read.xlsx？

我创建了一个示例* .xlsx文件：

> library(xlsx)
> d1 = data.frame(A=LETTERS[1:3], B=letters[1:3], C=1:3, D=c(1.1, NA, NA))
> str(d1)
'data.frame':   3 obs. of  4 variables:
 $ A: Factor w/ 3 levels "A","B","C": 1 2 3
 $ B: Factor w/ 3 levels "a","b","c": 1 2 3
 $ C: int  1 2 3
 $ D: num  1.1 NA NA
> write.xlsx(d1, 'test.xlsx', sheetName='Sheet1', row.names=F, showNA=F)

然后尝试用read.xlsx读取它，不带colClasses参数：

> d2 = read.xlsx('test.xlsx', sheetName='Sheet1')
> str(d2)
'data.frame':   3 obs. of  4 variables:
 $ A: Factor w/ 3 levels "A","B","C": 1 2 3
 $ B: Factor w/ 3 levels "a","b","c": 1 2 3
 $ C: num  1 2 3
 $ D: num  1.1 NA NA
> d2 = read.xlsx('test.xlsx', sheetName='Sheet1', colClasses=c(B='character', 'A'='character'))
> str(d2)
'data.frame':   3 obs. of  4 variables:
 $ A: Factor w/ 3 levels "A","B","C": 1 2 3
 $ B: Factor w/ 3 levels "a","b","c": 1 2 3
 $ C: num  1 2 3
 $ D: num  1.1 NA NA

问题是colClasses似乎没有效果。有什么想法吗？

感谢您的帮助。

阿列克谢

P.S。我有R 3.0.1，xlsx 0.5.1

Answer 1

colClasses=正在运行，但问题是当导入数据要将字符列转换为因子时，系统默认操作。

如果您导入test.xlsx并将所有列设置为"character"，则会看到所有列都是因素（也是数字）。

d2 = read.xlsx('test.xlsx', sheetName='Sheet1', colClasses=rep("character",4))
 str(d2)
'data.frame':   3 obs. of  4 variables:
 $ A: Factor w/ 3 levels "A","B","C": 1 2 3
 $ B: Factor w/ 3 levels "a","b","c": 1 2 3
 $ C: Factor w/ 3 levels "1","2","3": 1 2 3
 $ D: Factor w/ 1 level "1.1": 1 NA NA

为确保不将字符转换为因子，您可以将参数stringsAsFactors=FALSE添加到函数read.xlsx()。

d2 = read.xlsx('test.xlsx', sheetName='Sheet1', 
                colClasses=c(B='character', A='character'),stringsAsFactors=FALSE)

str(d2)
'data.frame':   3 obs. of  4 variables:
 $ A: chr  "A" "B" "C"
 $ B: chr  "a" "b" "c"
 $ C: num  1 2 3
 $ D: num  1.1 NA NA