July 2017
Intermediate to advanced
398 pages
11h 54m
Chinese
Content preview from Python数据处理
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186
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第
9
章
成为空值。如果
table_b
中有值没有在
table_a
中匹配，它们会被排除在新表之外。选择
哪一张表在前面和使用哪一种方式的联结是非常重要的。
我们绝不想要空值存在。我们的问题围绕数据是怎样关联的，为了达到这个目的，我们想
要使用内联结。
agate
库的
join
方法允许传递
inner=True
参数，这会使函数仅作内联结，
只保留匹配的行，不会在联结后有空值行。
我们尝试联结童工数据和新规整后的
cpi_table
。当我们查看这两个表时，可以将它们通
过国家
/
领土的名称匹配在一起。在
cpi_table
中，我们有
Country/Territory
列，同时，在
童工数据中，我们有
Counties and areas
列。为了联结这两张表，运行下面的代码
:
cpi_and_cl = cpi_table.join(ranked, 'Country / Territory',
'Countries and areas', inner=True)
将匹配行放到新表
cpi_and_cl
中。我们可以通过打印几个值来查看这张表，同时研究新的
联结后的列，像下面代码这样：
cpi_and_cl.column_names
for
r
in
cpi_and_cl.order_by('CPI 2013 Score').limit(10).rows:
print
'{}: {} - {}%'.format(r['Country / Territory'],
r['CPI 2013 Score'], r['Total ...
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