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

问题描述

证明有一个像,,,,

地图文本

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

然后，如果我尝试找到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.

谢谢你.

推荐答案

不需要GENERATE一个字段然后在FILTER中使用它；您可以将其包含在 FILTER 语句中以开始:

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;

在您的数据上，这将返回一条记录:

On your data, this returns one record:

([key2#v2])

附带说明，如果空字符串是有效值，您可能更愿意使用的标准是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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