警告消息：在rbindlist（allargs）：强制引入的NAs：data.table中可能的错误？ [英] Warning message: in rbindlist(allargs) : NAs introduced by coercion: possible bug in data.table?

问题描述

在分析一些数据时，我发现了警告消息，我怀疑这是一个错误，因为它是一个很简单的命令，我已经工作过很多次。

While analysing some data, I came across the warning message, which I suspect to be a bug as it is a pretty straightforward command that I have worked with many times.

Warning message:
In rbindlist(allargs) : NAs introduced by coercion

我能够重现错误。

# unique random names for column V1
set.seed(45)
n <- sapply(1:500, function(x) {
    paste(sample(c(letters[1:26]), 10), collapse="")
})
# generate some values for V2 and V3
dt <- data.table(V1 = sample(n, 30*500, replace = TRUE), 
                 V2 = sample(1:10, 30*500, replace = TRUE), 
                 V3 = sample(50:100, 30*500, replace = TRUE))
setkey(dt, "V1")

# No warning when providing column names (and right results)
dt[, list(s = sum(V2), m = mean(V3)),by=V1]

#              V1   s        m
#   1: acgmqyuwpe 238 74.97778
#   2: adcltygwsq 204 79.94118
#   3: adftozibnh 165 75.51515
#   4: aeuowtlskr 164 75.70968
#   5: ahfoqclkpg 192 73.20000
#  ---                        
# 496: zuqegoxkpi  93 77.95000
# 497: zwpserimgf 178 72.62963
# 498: zxkpdrlcsf 154 78.04167
# 499: zxvoaeflhq 121 75.34615
# 500: zyiwcsanlm 180 76.61290

# Warning message and results with NA
dt[, list(sum(V2), mean(V3)),by=V1]

#              V1  V1       V2
#   1: acgmqyuwpe 238 74.97778
#   2: adcltygwsq 204 79.94118
#   3: adftozibnh 165 75.51515
#   4: aeuowtlskr 164 75.70968
#   5: ahfoqclkpg 192 73.20000
#  ---                        
# 496: zuqegoxkpi  NA 77.95000
# 497: zwpserimgf  NA 72.62963
# 498: zxkpdrlcsf  NA 78.04167
# 499: zxvoaeflhq  NA 75.34615
# 500: zyiwcsanlm  NA 76.61290

Warning message:
In rbindlist(allargs) : NAs introduced by coercion

• 1）

  • 1) It seems that this happens if you don't provide the column names.

    2）即使这样，当 V1 你在 by = 中使用有很多独特的条目（此处为500），并且不指定列名，那么这似乎发生了。也就是说，当 by = 列 V1 有 较少的唯一条目。例如，尝试将 n 的代码从 sapply（1：500，... ）更改为 sapply（1:50，... ，您不会收到警告。

    2) Even then, in particular, when V1 (or the column you use in by=) has a lot of unique entries (500 here) and you don't specify column names, then this seems to happen. That is, this DOES NOT happen when the by= column V1 has fewer unique entries. For example, try changing the code for n from sapply(1:500, ... to sapply(1:50, ... and you'll get no warning.

    这里发生了什么？它的R版本2.15在Macbook pro与OS X 10.8.2（虽然我测试它在另一个macbook pro与2.15.2）。这是 sessionInfo（）。

    What's going on here? Its R version 2.15 on Macbook pro with OS X 10.8.2 (although I tested it on another macbook pro with 2.15.2). Here's the sessionInfo().

    > sessionInfo()
    R version 2.15.0 (2012-03-30)
    Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
    
    locale:
    [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
    
    attached base packages:
    [1] stats     graphics  grDevices utils     datasets  methods   base     
    
    other attached packages:
    [1] data.table_1.8.6 reshape2_1.2.2  
    
    loaded via a namespace (and not attached):
    [1] plyr_1.8      stringr_0.6.2 tools_2.15.0 
    

    只需复制 2.15.2 ：

    > sessionInfo()
    R version 2.15.2 (2012-10-26)
    Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
    
    locale:
    [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
    
    attached base packages:
    [1] stats     graphics  grDevices utils     datasets  methods   base     
    
    other attached packages:
    [1] data.table_1.8.6
    

    
    

    推荐答案

    更新：现在由Ricardo修正为v1.8.9

    
    

    .tables包含重复，或NA列名
    现在可以工作，＃2726& ＃2384。感谢Garrett See和Arun Srinivasan
    报告。这也影响了使用
    重复的列名称打印data.tables，因为头部和尾部在内部rbinded在一起
    。

    o rbind'ing data.tables containing duplicate, "" or NA column names now works, #2726 & #2384. Thanks to Garrett See and Arun Srinivasan for reporting. This also affected the printing of data.tables with duplicate column names since the head and tail are rbind-ed together internally.

    
    
    

    ---

    
    
    

    是的，错误。看起来是在具有重复名称的 data.table 的打印方法中。

    ans = dt[, list(sum(V2), mean(V3)),by=V1]
    head(ans)
               V1  V1       V2     # notice the duplicated V1
    1: acgmqyuwpe 140 78.07692
    2: adcltygwsq 191 76.93333
    3: adftozibnh 153 73.82143
    4: aeuowtlskr 122 73.04348
    5: ahfoqclkpg 143 75.83333
    6: ahtczyuipw 135 73.54167
    tail(ans)
               V1  V1       V2
    1: zugrnehpmq 189 72.63889
    2: zuqegoxkpi 150 76.03333
    3: zwpserimgf 180 74.81818
    4: zxkpdrlcsf 115 72.57895
    5: zxvoaeflhq 157 76.53571
    6: zyiwcsanlm 145 72.79167
    print(ans)
    Error in rbindlist(allargs) : 
        (converted from warning) NAs introduced by coercion
    rbind(head(ans),tail(ans))
    Error in rbindlist(allargs) : 
        (converted from warning) NAs introduced by coercion
    

    要解决这个问题，不要使用列名 V1 code> V2 等。

    As a work around, don't create data.table with column names V1, V2 etc.

    这是由于这个已知的错误：

    It's arising due to this known bug :

    ＃2384包含重复列名的表格的rbind不正确绑定

    我已在其中添加了此问题的链接。

    and I've added a link there back to this question.

    谢谢！

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