Python - 按字典分组

Question

我正在使用 Python 3.5，并且我有以下 dics 数组：

d1 = [{id=1, col="name", oldvalue="foo", newvalue="bar"}, {id=1, col="age", oldvalue="25", newvalue="26"}, {id=2, col="name", oldvalue="foo", newvalue="foobar"}, {id=3, col="age", oldvalue="25", newvalue="26"}]

d2 = [{id=1, col="name", oldvalue="foo", newvalue="bar"}, {id=1, col="age", oldvalue="25"]

d3 = [{id=3, col="age", oldvalue="25", newvalue="26"}]

如您所见，它显示了对特定“行”所做的一些更改。

我想知道是否有办法返回更新的总行数，所以：

def counting_updates(d):
    # ...
    return total

print counting_updates(d1) # prints 3 because 3 rows were updated
print counting_updates(d2) # prints 1 because 1 row was updated
print counting_updates(d3) # prints 1 because 1 row was updated

Answer 1

如果您正在寻找唯一 ids 的数量，那么

len({row['id'] for row in d})

{} 是一个集合理解。