生成汇总(“枢轴"?)表 [英] Produce a summary ("pivot"?) table

问题描述

我想要一种汇总数据库表的方法，以便将共享公共 ID 的行汇总到一行输出中.

I'd like a way to summarise a database table so that rows sharing a common ID are summarised into one row of output.

我的工具是 SQLite 和 Python 2.x.

My tools are SQLite and Python 2.x.

例如，下面是我当地超市的水果价格表...

For example, given the following table of fruit prices at my local supermarkets...

+--------------------+--------------------+--------------------+
|Fruit               |Shop                |Price               |
+--------------------+--------------------+--------------------+
|Apple               |Coles               |$1.50               |
|Apple               |Woolworths          |$1.60               |
|Apple               |IGA                 |$1.70               |
|Banana              |Coles               |$0.50               |
|Banana              |Woolworths          |$0.60               |
|Banana              |IGA                 |$0.70               |
|Cherry              |Coles               |$5.00               |
|Date                |Coles               |$2.00               |
|Date                |Woolworths          |$2.10               |
|Elderberry          |IGA                 |$10.00              |
+--------------------+--------------------+--------------------+

... 我想制作一个汇总表，显示每个超市每种水果的价格.空格应由 NULL 填充.

... I want to produce a summary table showing me the price of each fruit at each supermarket. Blank spaces should be filled by NULLs.

+----------+----------+----------+----------+
|Fruit     |Coles     |Woolworths|IGA       |
+----------+----------+----------+----------+
|Apple     |$1.50     |$1.60     |$1.70     |
|Banana    |$0.50     |$0.60     |$0.70     |
|Cherry    |NULL      |$5.00     |NULL      |
|Date      |$2.00     |$2.10     |NULL      |
|Elderberry|NULL      |NULL      |$10.00    |
+----------+----------+----------+----------+

我相信文献将其称为数据透视表"或数据透视查询"，但显然 SQLite 没有t 支持 PIVOT.(该问题的解决方案使用硬编码的 LEFT JOIN s.这对我来说并不真正吸引我，因为我不知道列"名称.)

I believe the literature calls this a "pivot table" or a "pivot query", but apparently SQLite doesn't support PIVOT. (The solution in that question uses hardcoded LEFT JOINs. This doesn't really appeal to me because I don't know the "column" names in advance.)

现在我通过在 Python 中遍历整个表并累积 dicts 的 dict 来做到这一点，这有点笨拙.我对更好的解决方案持开放态度，无论是 Python 还是 SQLite，都会以表格形式提供数据.

Right now I do this by iterating through the entire table in Python and accumulating a dict of dicts, which is a bit klutzy. I am open to better solutions, either in Python or SQLite, that will give the data in tabular form.

推荐答案

在 python 方面，你可以使用一些 itertools 魔法来重新排列你的数据:

On python side, you could use some itertools magic for rearranging your data:

data = [('Apple',      'Coles',      1.50),
        ('Apple',      'Woolworths', 1.60),
        ('Apple',      'IGA',        1.70),
        ('Banana',     'Coles',      0.50),
        ('Banana',     'Woolworths', 0.60),
        ('Banana',     'IGA',        0.70),
        ('Cherry',     'Coles',      5.00),
        ('Date',       'Coles',      2.00),
        ('Date',       'Woolworths', 2.10),
        ('Elderberry', 'IGA',        10.00)]

from itertools import groupby, islice
from operator import itemgetter
from collections import defaultdict

stores = sorted(set(row[1] for row in data))
# probably splitting this up in multiple lines would be more readable
pivot = ((fruit, defaultdict(lambda: None, (islice(d, 1, None) for d in data))) for fruit, data in groupby(sorted(data), itemgetter(0)))

print 'Fruit'.ljust(12), '\t'.join(stores)
for fruit, prices in pivot:
    print fruit.ljust(12), '\t'.join(str(prices[s]) for s in stores)

<小时>

输出:

Fruit        Coles      IGA     Woolw
Apple        1.5        1.7     1.6
Banana       0.5        0.7     0.6
Cherry       5.0        None    None
Date         2.0        None    2.1
Elderberry   None       10.0    None

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