将元素附加到关联数组awk [英] Appending an element to associative array awk

问题描述

我有一个包含几个字段的输入文件(input.txt):

I've got an input file (input.txt) with a few fields:

A1  B1  C1  D1  E1
A2  B2  C2  D1  E2
A3  B3  C3  D2  E3
A4  B4  C4  D2  E4

我想附加一个关联数组的元素

And I want to append elements of an associative array,

awk '{a[$4]=a[$4] $5; print a[$4]} END {for(b in a) {print a[b]}}' input.txt

我认为输出应该是(即E2连接到E1，E4连接到E3):

I think the output should be (ie E2 is concatenated to E1, and E4 is concatenated to E3):

E1 E2
E3 E4

，但是输出是:

E2
E4

我不确定我的代码有什么问题吗?

I'm not sure what's wrong with my code?

推荐答案

您的输出与您的命令不一致，但是我认为您需要以下内容:

Your output isn't consistent with your command, but I assume that you want the following:

• 为每个唯一的第4列值建立第5列值的列表
• 打印这些列表，并在其前面加上相应的第4列值

一个天真的解决方案来获得您想要的东西:

A naïve fix to get what you want would be:

$ awk '{a[$4]=a[$4] " " $5} END {for (b in a) { print b; print a[b]}}' input.txt
D1
 E1 E2
D2
 E3 E4

但是有两点需要注意:

• 第5列的累积值将有一个前导空格-在这种情况下碰巧有助于分组输出.
• 由于用for (b in a)枚举键，所以第4列值将不会按照它们在输入中出现的顺序出现，因为awk枚举其[always asociative]数组的键的顺序是基于内部哈希值，该值与添加的顺序没有保证的关系(通常也不保证任何特定的顺序).

• The accumulated 5-th column values will have a leading space - which happens to help with grouped output in this case.
• Due to enumerating the keys with for (b in a), the 4th-column values will NOT appear in the order they appear in the input, because the order in which awk enumerates keys of its [always associative] arrays is based on internal hash values, which has no guaranteed relationship to the order in which array elements were added (nor does it guarantee any particular order in general).

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