R中带有data.table的非等值联接-反引号列名称问题 [英] non-equi-joins in R with data.table - backticked column name trouble

问题描述

当（反引号）列名称包含空格时，我无法与data.table进行非等联接。

I can't manage to do a non-equi-join with data.table when (backticked) column names include a space.

我从我们的数据库在工作，我们明确的政策是让每个人都使用相同的名称以避免混淆。我当然可以进行转换和重新转换，但是我希望避免这种情况。

I collect such names from our database at work, and our explicit policy is for everyone to use those same names to avoid confusion. I could of course convert and reconvert, but I'd prefer to avoid that.

我想知道这是否是data.table中的一个小故障，如果可以的话，可以吗？补救？还是我错过了什么？我对R很陌生，所以完全有可能...

I wonder, is this a glitch in data.table, and if so, can it be remedied? Or am I missing something? I'm quite new to R, so the latter is entirely possible...

一个可重现的示例：

以下的方法可以工作：

a <- data.table(`test name1` = c('A', 'A', 'A', 'B', 'B'),
                 `test_name2` = c(1,2,3,3,4))

b <- data.table(`test_name3` = c(0,1,2),
                 `test name4` = c('A', 'A', 'B'),
                 V2 = c(1,2,3),
                 V3 = c('Low', 'Medium', 'High'))

a[b, on = .(`test name1` = `test name4`, `test_name2` > `test_name3`, `test_name2` <= V2)]

以下内容不是：

a <- data.table(`test name1` = c('A', 'A', 'A', 'B', 'B'),
                 `test name2` = c(1,2,3,3,4))

b <- data.table(`test name3` = c(0,1,2),
                 `test name4` = c('A', 'A', 'B'),
                 V2 = c(1,2,3),
                 V3 = c('Low', 'Medium', 'High'))

a[b, on = .(`test name1` = `test name4`, `test name2` > `test name3`, `test name2` <= V2)]

错误消息是：

[。data.table （a，b，on =。（ 测试名称1 = 测试名称4 ，测试名称2 >：
在x

Error in [.data.table(a, b, on = .(test name1 = test name4, test name2 > : Column(s) [test name2,test name2] not found in x

sessionInfo（）：

sessionInfo():

R version 3.3.2 (2016-10-31)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=Norwegian (Bokmål)_Norway.1252  LC_CTYPE=Norwegian (Bokmål)_Norway.1252    LC_MONETARY=Norwegian (Bokmål)_Norway.1252
[4] LC_NUMERIC=C                               LC_TIME=Norwegian (Bokmål)_Norway.1252    

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

other attached packages:
[1] data.table_1.11.4

推荐答案

用字符串指定 on = 是另一种选择：

Specifying on= with strings is another option:

a[b, on = c("test name1==test name4", "test name2>test name3", "test name2<=V2")]

我认为只有在没有在等号/不等号运算符和 == 周围使用空格，而不是 = 。

I think this works only if there is no whitespace around the equality/inequality operators and == is used instead of =.

我不确定是否可以按照OP的代码编写 on = 的方法，尽管似乎应该这样做。

I'm not sure if there's a way to write the on= along the lines of the OP's code, though it seems like there should be.

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