在Unix Join操作中填充空白字段 [英] Padding Empty Field in Unix Join Operation

问题描述

我有两个要在其中执行联合操作的文件 根据第一栏:

I have two files where I want to perform union operation based on 1st column:

file1.txt

file1.txt

foo 1
bar 2
qux 3

file2.txt

file2.txt

foo x
qux y
boo z

我希望得到的结果是这样的:

The result I hope to get is like this:

foo  1 x
bar  2 -
qux  3 y
boo  - z

填充第1列的空白字段 与-".

where the empty fields of column 1 is padded with "-".

但是为什么这个加入命令不能按我预期的那样工作?

But why this join command doesn't work as I expected?

$ join -a1 -a2 -e"-" file1.txt file2.txt

什么是正确的方法?

推荐答案

"重要:FILE1和FILE2必须在连接字段上排序."(摘自此在线联机帮助页).

"Important: FILE1 and FILE2 must be sorted on the join fields." (from this online manpage).

此问题#1.问题2更为严重:选项-e的文献记载不充分-仅与-o结合使用，因此例如:

This problem #1. Problem #2 is worse: option -e is badly documented -- only works in conjunction with -o, so for example:

$ join -a 1 -a 2 -e'-' -o '0,1.2,2.2' sfile1.txt sfile2.txt
bar 2 -
boo - z
foo 1 x
qux 3 y

其中s前缀名称表示我事先sort已存储的文件.

where the s prefix name indicated files that I've sorted beforehand.

man join解释了-o开关(我在上面指向的联机帮助页也是如此).它指定要输出的字段(1.2表示文件1和c中的第二个字段)，或0表示连接字段，并且是逗号分隔的列表. (实际上，我不记得0的值，因此最初给出的笨拙解决方案需要awk后处理，但是当前的解决方案更好……不需要awk！).

man join explains the -o switch (so does the online manpage I point to above). It specifies the fields to output (1.2 means 2nd field from file 1, &c), or 0 to mean the join field, and is a comma-separated list. (I didn't remember the 0 value, actually, so had originally given a clumsier solution requiring awk post-processing, but the current solution is better... and no awk needed!).

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