August 2022
Beginner to intermediate
463 pages
9h 22m
Chinese
Content preview from Tableau Prep即学即用
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｜
243
空值处理
图
27
-
1
：Volume（数量）数据字段中的空值
现在你知道了它们是什么以及在哪里可以找到它们，让我们看看什么时候可以接受
数据集中的空记录，什么时候应该删除或替换它们。
27.2
什么时候可以接受空值
为了了解什么时候可以接受空值，我们来评估一下空值的影响。最常见的空值会影
响分析的情况，就是当你对数值进行求平均运算时。图
27-2
展示了一个有空值的简
单数据集，图
27-3
展示了同样的数据集，但用数字
0
（零值）代替了空值。
图
27
-
2
：有空值的香皂数据集
244
｜
第
27
章
图
27
-
3
：带零值的香皂数据集
如果你在
Prep Builder
中以完全相同的方式使用这两个表来计算平均值，由于空
值的影响，它们将产生两种不同的输出。例如，在
Input
（输入）步骤之后添加
Aggregate
（汇总）步骤，计算每种类型产品的平均
Volume
（数量），会产生完
全不一样的结果。当你将这种技术应用于有空值的数据集时，
Bars
（条形皂）和
Liquid
（液体皂）返回的值分别是
56.6
和
566.6
（见图
27-4
）。
图
27
-
4
：数据集中有空值时所产生的平均值
然而，将同样的技术应用于包含数据
0
（零值）的表格，得到的结果是，条形皂的
结果为
42.5
，液体皂的结果为
425
（见图
27-5
）。
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.