我可以在hadoop-PIG中对Map结构使用"filter by"吗? [英] Can I use "filter by' with Map structure in hadoop - PIG?

问题描述

证明其中有一个地图，

map.text

[key1#v1]
[key2#v2]
[key3#v3]

然后，如果我尝试查找'key2'的值，

then, if I try to find 'value of 'key2'',

A = load ‘map.text’ as (M:map[]);
B = foreach A generate M#'key2';
C = filter B by $0!='';     // to get rid of empty value like (), (), ().
dump C;

还有其他方法可以找到key2吗?仅使用过滤依据".

is there any other way to find key2? with using 'filter by' only.

谢谢.

推荐答案

不需要GENERATE字段，然后在FILTER中使用它；您可以将其包含在FILTER语句中，开头为:

There is no need to GENERATE a field and then use it in a FILTER; you can include it in the FILTER statement to begin with:

A = load 'map.text' as (M:map[]);
B = filter A by M#'key2' != '';
dump B;

根据您的数据，这将返回一条记录:

On your data, this returns one record:

([key2#v2])

请注意，万一空字符串是有效值，则您宁愿使用的标准是by M#'key2' is not null.

As a side note, in case empty strings are ever valid values, the criterion you might rather use is by M#'key2' is not null.

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