向下填充具有NA的列(具有R base或data.table)

Question

我想使用人口普查的县邻接数据,但我坚持把它变成一个很好的形式.数据分为四列:第一个县,第一个代码,第二个县,第二个代码.第一个县列不重复,而是以我现在阅读的方式取值"":

                     c1   cd1                    c2   cd2
1   Alamance County, NC 37001   Alamance County, NC 37001
2                          NA    Caswell County, NC 37033
3                          NA    Chatham County, NC 37037
4                          NA   Guilford County, NC 37081
5                          NA     Orange County, NC 37135
6                          NA   Randolph County, NC 37151
7                          NA Rockingham County, NC 37157
8  Alexander County, NC 37003  Alexander County, NC 37003
9                          NA   Caldwell County, NC 37027
10                         NA    Catawba County, NC 37035
11                         NA    Iredell County, NC 37097
12                         NA     Wilkes County, NC 37193
13 Alleghany County, NC 37005  Alleghany County, NC 37005
14                         NA       Ashe County, NC 37009
15                         NA      Surry County, NC 37171
16                         NA     Wilkes County, NC 37193
17                         NA    Grayson County, VA 51077
18     Anson County, NC 37007      Anson County, NC 37007
19                         NA Montgomery County, NC 37123
20                         NA   Richmond County, NC 37153

我碰巧只对该链接中找到的北卡罗来纳州部分数据感兴趣,其中一部分就是您在上面看到的内容:

#
nc_cc <- structure(list(c1 = c("Alamance County, NC", "", "", "", "", "", "", "Alexander County, NC", "", "", "", "", "Alleghany County, NC", "", "", "", "", "Anson County, NC", "", ""), cd1 = c(37001L, NA, NA, NA, NA, NA, NA, 37003L, NA, NA, NA, NA, 37005L, NA, NA, NA, NA, 37007L, NA, NA), c2 = c("Alamance County, NC", "Caswell County, NC", "Chatham County, NC", "Guilford County, NC", "Orange County, NC", "Randolph County, NC", "Rockingham County, NC", "Alexander County, NC", "Caldwell County, NC", "Catawba County, NC", "Iredell County, NC", "Wilkes County, NC", "Alleghany County, NC", "Ashe County, NC", "Surry County, NC", "Wilkes County, NC", "Grayson County, VA", "Anson County, NC", "Montgomery County, NC", "Richmond County, NC" ), cd2 = c(37001L, 37033L, 37037L, 37081L, 37135L, 37151L, 37157L, 37003L, 37027L, 37035L, 37097L, 37193L, 37005L, 37009L, 37171L, 37193L, 51077L, 37007L, 37123L, 37153L)), .Names = c("c1", "cd1", "c2", "cd2"), row.names = c(NA, 20L), class = "data.frame")
#

我想要一个干净的邻接关联(并且县名是多余的),所以我想要的输出可以采用多种形式:data.frame,list,...

我想出的原始解决方案(经过深思熟虑)是这样的:

require(data.table)
DT <- data.table(nc_cc)
DT[,list(cd1=cd1[1],cd2),by=cumsum(!is.na(cd1))][,list(cd1,cd2)]

给

      cd1   cd2
 1: 37001 37001
 2: 37001 37033
 3: 37001 37037
 4: 37001 37081
 5: 37001 37135
 6: 37001 37151
 7: 37001 37157
 8: 37003 37003
 9: 37003 37027
10: 37003 37035
11: 37003 37097
12: 37003 37193
13: 37005 37005
14: 37005 37009
15: 37005 37171
16: 37005 37193
17: 37005 51077
18: 37007 37007
19: 37007 37123
20: 37007 37153

我已将其标记为data.table因为我在上面的解决方案中使用了它,我怀疑有一些可以做的好事roll.真的,我从来没有理解过这些文档roll,所以我希望在这里学到一些东西......所以:这可以做得更好吗？

编辑: 这个问题是同样的问题,所以我将我的问题修改为:"有没有更好的方法来使用data.table或基础R(因为我反对安装更多的包)？"

Answer 1

一个非常标准的方法是:

library(data.table)
dt = data.table(nc_cc)

dt[, cd1 := cd1[1], by = cumsum(!is.na(cd1))]