同时向前和向后滚动 data.table

Question

这与上一个关于 SO 的问题有关:roll data.table with rollends

鉴于数据...

library(data.table)

dt1 = data.table(Date=seq(from=as.Date("2013-01-03"),
                      to=as.Date("2013-06-27"), by="1 week"),
             key="Date")[, ind:=.I]
dt2 = data.table(Date=seq(from=as.Date("2013-01-01"),
                      to=as.Date("2013-06-30"), by="1 day"),
             key="Date")

我尝试 将每周数据点向前和向后移动一天 ...

dt1[dt2, roll=1][dt2, roll=-1]

...但只有第一个滚动连接(向前)似乎有效， roll=-1被忽略:

           Date ind
  1: 2013-01-01  NA
  2: 2013-01-02  NA
  3: 2013-01-03   1
  4: 2013-01-04   1
  5: 2013-01-05  NA
 ---               
177: 2013-06-26  NA
178: 2013-06-27  26
179: 2013-06-28  26
180: 2013-06-29  NA
181: 2013-06-30  NA

当我颠倒顺序时，效果相同:

dt1[dt2, roll=-1][dt2, roll=1]

           Date ind
  1: 2013-01-01  NA
  2: 2013-01-02   1
  3: 2013-01-03   1
  4: 2013-01-04  NA
  5: 2013-01-05  NA
 ---               
177: 2013-06-26  26
178: 2013-06-27  26
179: 2013-06-28  NA
180: 2013-06-29  NA
181: 2013-06-30  NA

我想实现:

           Date ind
  1: 2013-01-01  NA
  2: 2013-01-02   1
  3: 2013-01-03   1
  4: 2013-01-04   1
  5: 2013-01-05  NA
 ---               
177: 2013-06-26  26
178: 2013-06-27  26
179: 2013-06-28  26
180: 2013-06-29  NA
181: 2013-06-30  NA

编辑:
我用的是新鲜的 数据表版本 1.8.11 ，注意 session 细节:

sessionInfo()

R version 3.0.0 (2013-04-03)
Platform: x86_64-w64-mingw32/x64 (64-bit)

locale:
[1] LC_COLLATE=English_United Kingdom.1252  LC_CTYPE=English_United Kingdom.1252   
[3] LC_MONETARY=English_United Kingdom.1252 LC_NUMERIC=C                           
[5] LC_TIME=English_United Kingdom.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.8.11

loaded via a namespace (and not attached):
[1] plyr_1.8       reshape2_1.2.2 stringr_0.6.2  tools_3.0.0   

谢谢

Answer 1

第一次加入后没有什么可滚动的，每一行都在dt2 有 dt1[dt2, roll = .] 中的相应行.所以只需分别做两个卷并将它们组合在一起，例如:

dt1[dt2, roll = 1][, ind := ifelse(is.na(ind), dt1[dt2, roll = -1]$ind, ind)]