Question

我无法对我的数据使用tableB [tableA]产生预期的结果。但是在简单的示例数据上也可以正常工作。请解码我在做什么错。

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这是预期的。但是..


> tableA <- data.table(col1 = c( 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6,        1.7, 1.8, 1.9), key = 'col1')

> tableA
    col1
 1:  1.0
 2:  1.1
 3:  1.2
 4:  1.3
 5:  1.4
 6:  1.5
 7:  1.6
 8:  1.7
 9:  1.8
10:  1.9

> tableB <- data.table(col1 = c( 1.0, 1.2, 1.5, 1.9), col2 = c( "A", "B", "C", "D"), col3 = c( "AA", "BB", "CC", "DD"), key = 'col1')

> tableB
   col1 col2 col3
1:  1.0    A   AA
2:  1.2    B   BB
3:  1.5    C   CC
4:  1.9    D   DD

> tableA <- tableB[ tableA]

> tableA
    col1 col2 col3
 1:  1.0    A   AA
 2:  1.1 <NA> <NA>
 3:  1.2    B   BB
 4:  1.3 <NA> <NA>
 5:  1.4 <NA> <NA>
 6:  1.5    C   CC
 7:  1.6 <NA> <NA>
 8:  1.7 <NA> <NA>
 9:  1.8 <NA> <NA>
10:  1.9    D   DD

它不是任何“错别字”。我可以一次又一次地复制相同的精确结果。任何见解都是有价值的。

没有错误。我期望16个有效行和4个NA行。但是，我只得到13个有效行和7个NA行。

Answer 1

这是由于V1中十进制值的浮点错误。这不是R（或data.table）问题，而仅仅是计算机使用十进制数字的方式。
请阅读：Why are these numbers not equal?，以了解更多信息。

为防止此类“错误”，一种解决方案是将联接列设置为字符。

NA

将给出预期的结果

tableA[, V1 := as.character(V1)]
tableB[, V1 := as.character(V1)]

tableB[tableA, on = .(V1)]

无法复制tableB [tableA]的预期结果

1 个答案: