为什么所有日期字符串都变成了数字？

Question

start=as.Date("2013-09-02")
x[1:140]<-start
for(i in 2:140){
  x[i]<-x[i-1]+1 }

我得到的是这样的东西:

[1] "2013-09-02" "2013-09-03" "2013-09-04" "2013-09-05" "2013-09-06"    

当我跑:

y<-matrix(x,nrow=20,byrow=TRUE) 
> y

   [,1]  [,2]  [,3]  [,4]  [,5]  [,6]  [,7]
 [1,] 15950 15951 15952 15953 15954 15955 15956   

所有的字符串都变成了数字,为什么？我怎么能不在y中改变它们？

Answer 1

问题是R不允许使用日期填充矩阵.这两个"matrix"和"Date"是类.R中Date对象的底层表示只是一个整数.因此,当您创建矩阵时y,它会从中获取基础数据x(这是一个整数数组),添加维度属性并生成类"matrix".

这个问题没有任何干净的方法.但是,你可以使用一些黑客.例如,你可以明确地强制y将类"Date"以及"matrix"有class(y)<-c("matrix","Date"). y仍然会打印出日期的矢量,但你可以使用矩阵坐标来操纵它:

> class(y)<-c("matrix","Date")
> head(y)
 [1] "2013-09-02" "2013-09-09" "2013-09-16" "2013-09-23" "2013-09-30"
 [6] "2013-10-07" "2013-09-03" "2013-09-10" "2013-09-17" "2013-09-24"
[11] "2013-10-01" "2013-10-08" "2013-09-04" "2013-09-11" "2013-09-18"
[16] "2013-09-25" "2013-10-02" "2013-10-09" "2013-09-05" "2013-09-12"
[21] "2013-09-19" "2013-09-26" "2013-10-03" "2013-10-10" "2013-09-06"
[26] "2013-09-13" "2013-09-20" "2013-09-27" "2013-10-04" "2013-10-11"
[31] "2013-09-07" "2013-09-14" "2013-09-21" "2013-09-28" "2013-10-05"
[36] "2013-10-12" "2013-09-08" "2013-09-15" "2013-09-22" "2013-09-29"
[41] "2013-10-06" "2013-10-13"
> y[1,]
[1] "2013-09-02" "2013-09-03" "2013-09-04" "2013-09-05" "2013-09-06"
[6] "2013-09-07" "2013-09-08"
> y[1,]<-y[1,]+1
> y[1,]
[1] "2013-09-03" "2013-09-04" "2013-09-05" "2013-09-06" "2013-09-07"
[6] "2013-09-08" "2013-09-09"

您还可以使用数据框而不是矩阵:

> y<-data.frame(y)
> y<-data.frame(lapply(y,function(x) {class(x)<-"Date";x}))
> head(y)
          X1         X2         X3         X4         X5         X6         X7
1 2013-09-02 2013-09-03 2013-09-04 2013-09-05 2013-09-06 2013-09-07 2013-09-08
2 2013-09-09 2013-09-10 2013-09-11 2013-09-12 2013-09-13 2013-09-14 2013-09-15
3 2013-09-16 2013-09-17 2013-09-18 2013-09-19 2013-09-20 2013-09-21 2013-09-22
4 2013-09-23 2013-09-24 2013-09-25 2013-09-26 2013-09-27 2013-09-28 2013-09-29
5 2013-09-30 2013-10-01 2013-10-02 2013-10-03 2013-10-04 2013-10-05 2013-10-06
6 2013-10-07 2013-10-08 2013-10-09 2013-10-10 2013-10-11 2013-10-12 2013-10-13

第三种可能性是将元素保持为y字符格式,然后as.Date在需要时将它们转换为日期:

> y<-matrix(as.character(x),nrow=20,byrow=T)
> head(y)
     [,1]         [,2]         [,3]         [,4]         [,5]        
[1,] "2013-09-02" "2013-09-03" "2013-09-04" "2013-09-05" "2013-09-06"
[2,] "2013-09-09" "2013-09-10" "2013-09-11" "2013-09-12" "2013-09-13"
[3,] "2013-09-16" "2013-09-17" "2013-09-18" "2013-09-19" "2013-09-20"
[4,] "2013-09-23" "2013-09-24" "2013-09-25" "2013-09-26" "2013-09-27"
[5,] "2013-09-30" "2013-10-01" "2013-10-02" "2013-10-03" "2013-10-04"
[6,] "2013-10-07" "2013-10-08" "2013-10-09" "2013-10-10" "2013-10-11"
     [,6]         [,7]        
[1,] "2013-09-07" "2013-09-08"
[2,] "2013-09-14" "2013-09-15"
[3,] "2013-09-21" "2013-09-22"
[4,] "2013-09-28" "2013-09-29"
[5,] "2013-10-05" "2013-10-06"
[6,] "2013-10-12" "2013-10-13"
> as.Date(y[1,])
[1] "2013-09-02" "2013-09-03" "2013-09-04" "2013-09-05" "2013-09-06"
[6] "2013-09-07" "2013-09-08"