需要帮助了解r data.table行为

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问题描述

我对data.table中的以下行为有些麻烦。

I am having a little trouble understanding the behavior of the following in data.table...

##Combine into one data.table
RecordNo <- 1:36
Record_Date <- c(31,33,38,41,44,59,68,69,75,78,85,88,
                         32,34,45,46,51,54,60,65,67,70,74,80,
                         33,35,42,45,50,60,65,70,75,80,82,85)
Cust_ID <- c(rep(1,12),rep(2,12),rep(3,12))
data <- data.table(RecordNo,Record_Date,Cust_ID)

##Create "list" of comparison dates
data[,list(Compare_Date=list(Record_Date)),by=c("Cust_ID")]

   Cust_ID       Compare_Date
1:       1 33,35,42,45,50,60,
2:       2 33,35,42,45,50,60,
3:       3 33,35,42,45,50,60,

上述代码输出日期列表对于每个Cust_ID，Cust_ID = 3。我希望有这样的输出。

The above code outputs the date list for Cust_ID=3 for each Cust_ID. I desire an output like this..

   Cust_ID       Compare_Date
1:       1 31,33,38,41,44,59,
2:       2 32,34,45,46,51,54,
3:       3 33,35,42,45,50,60,

data.table返回Cust_ID 3的日期列表而不是每个Cust_ID的正确值列表的任何想法？

Any ideas why data.table is returning the list of dates for Cust_ID 3 instead of the correct list of values for each Cust_ID?

sessionInfo()

R version 3.1.0 beta (2014-03-28 r65330)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8    LC_PAPER=en_US.UTF-8       LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

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

other attached packages:
[1] data.table_1.9.2

loaded via a namespace (and not attached):
[1] plyr_1.8.1     Rcpp_0.11.0    reshape2_1.2.2 stringr_0.6.2  tools_3.1.0

推荐答案

更新： c $ c> DT [，list（list（。）），通过=。] 有时导致错误的结果在R版本> = 3.1.0。现在，在中修正了 v1.9.3。从：

Update: The behaviour DT[, list(list(.)), by=.] sometimes resulted in wrong results in R version >= 3.1.0. This is now fixed in commit #1280 in the current development version of data.table v1.9.3. From NEWS:

有了这个修复，不再需要 I（）。

With this fix, there's no need for the I() anymore.

如果我在列表之前加入I，似乎可以工作：

Seems to work if I put in an "I" before the list:

##Create "list" of comparison dates
data[,list(Compare_Date=list(I(Record_Date))),by=c("Cust_ID")]

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