August 2022
Beginner to intermediate
463 pages
9h 22m
Chinese
Content preview from Tableau Prep即学即用
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｜
213
过滤
23.2.4
空值过滤
在
Null Values
（空值）选项中（同样从概况窗格中数据字段顶部的省略号菜单中进入），
可以选择是只保留包含
null
（空值）的行，还是保留具有
null-null
（非空值）的行（见
图
23-9
）。
图
23
-
9
：Null Values（空值）过滤器
23.3
何时过滤掉列
删除数据列是不应该轻视的数据准备步骤。一旦你做出了这个决定，几乎没有什么
办法能让这些数据从丢失的状态中恢复过来（除了之前步骤中一个令人困惑的连
接）。
尽管如此，在以下情况下，删除掉不必要的数据字段是很有价值的：
•
删除空白列。在使用
Excel
或文本文件时，会经常发现有明显的空白列，这些列
往往只在其中一行中暗藏着一个空格。删除这些，不用犹豫
!
•
删除那些大部分内容为
null
（空值）的列。仅仅因为某些行是空的，并不意味
着应该立即删除全部的列。有没有办法使用合并功能来填充这些行的数据？是
否有理由让该列包含空值？如果有，就把该列留在原地；否则，就把它过滤掉。
23.4
何时过滤掉行
与列一样，过滤掉数据行的原因有很多。注意不要删除别人在分析中可能发现有用
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