写一个把列表分组的函数

[ws0309]

写一个函数，接受两个参数，第一个参数是列表，第二个是个函数，返回的是按照这个函数作用到列表得到相同结果来分组的列表。比如：
gather(range(10), lambda x: x%3)
[[0, 3, 6, 9], [1, 4, 7], [2, 5, 8]]

gather(range(10), lambda x: x>3)
[[4, 5, 6, 7, 8, 9],[0, 1, 2, 3]]

gather(['a1','b2', 'c3', 'hello','bb'], lambda x: 'b' in x)
[['b2', 'bb'], ['a1', 'c3', 'hello']]

[bugs2k]

貌似用字典方式更方便：

def gather(alist, fn):
	tmp = {}
	for x in alist:
		y = fn(x)
		if y in tmp:
			tmp[y].append(x)
		else:
			tmp[y] = [x]
	return tmp

print gather(range(10), lambda x: x % 3)

[bugs2k]

def gather(alist, fn):
	tmax = 0
	for x in alist:
		y = fn(x)
		if y > tmax:
			tmax = y
	tmp = [[] for i in range(tmax + 1)]
	for x in alist:
		y = fn(x)
		tmp[y].append(x)
	return tmp

[angel_su]

试试itertools.groupby(iterable[, key])...

>>> import itertools
>>> def gather(iterable, key=None):
	data = sorted(iterable, key=key)
	return [list(g) for k, g in itertools.groupby(data, key)]

>>> gather(range(10), lambda x: x%3)
[[0, 3, 6, 9], [1, 4, 7], [2, 5, 8]]
>>> gather(range(10), lambda x: x>3)
[[0, 1, 2, 3], [4, 5, 6, 7, 8, 9]]
>>> gather(['a1','b2', 'c3', 'hello','bb'], lambda x: 'b' in x)
[['a1', 'c3', 'hello'], ['b2', 'bb']]
>>>

[chyanog]

def gather(seq, f):
    d = {}
    for x in seq:
        y=f(x)
        d[y]=d.get(y, [])+[x]
    return d

[ws0309]

尽量不用字典，而是用list来实现

[bugs2k]

def gather(alist, fn):
	tmp = []
	for x in alist:
		y = fn(x)
		try:
			t = tmp[y]
		except:
			z = y + 1
			w = len(tmp)
			if w < z:
				for i in range(w, z):
					tmp.append([])
		tmp[y].append(x)
	return tmp

[bugs2k]

def gather(alist, fn):
	tmp = []
	for x in alist:
		y = fn(x)
		z = y + 1
		w = len(tmp)
		if w < z:
			for i in range(w, z):
				tmp.append([])
		tmp[y].append(x)
	return tmp

[qq120848369]

[Quote=引用 4 楼 的回复:]

试试itertools.groupby(iterable[, key])...
Python code
>>> import itertools
>>> def gather(iterable, key=None):
data = sorted(iterable, key=key)
return [list(g) for k, g in itertools.groupby(d……
[/Quote]

这个函数坑不小, 一定要在sort和groupby时指定相同的key func.

The operation of groupby() is similar to the uniq filter in Unix. It generates a break or new group every time the value of the key function changes (which is why it is usually necessary to have sorted the data using the same key function). That behavior differs from SQL’s GROUP BY which aggregates common elements regardless of their input order.

[ws0309]

[Quote=引用 6 楼 的回复:]
Python code
def gather(alist, fn):
tmp = []
for x in alist:
y = fn(x)
z = y + 1
w = len(tmp)
if w < z:
for i in range(w, z):
……
[/Quote]
谢谢，

[chyanog]

def gather(seq, f):
    import collections
    d = collections.defaultdict(list)
    for x in seq:
        d[f(x)].append(x)
    return dict(d)

[chyanog]

def gather(seq,f):
    return [[i for i in seq if f(i)==j] for j in set(map(f,seq))]