mapreduce怎么写( 三 ) _mapreduce

3.怎么用Python写mapreduce,请举例说明,初学者,请赐教,不胜感激1.lambda # 匿名函数# 基本用法 lambda x: x**2 # 第一个参数，然后是表达式# 也可以使用如下（lambda x: x**2）(5)2. map() def map(function, sequence, *sequence_1): # real signature unknown; restored from __doc__ """ map(function, sequence[, sequence,。
]) -> list Return a list of the results of applying the function to the items of the argument sequence(s). If more than one sequence is given, the function is called with an argument list consisting of the corresponding item of each sequence, substituting None for missing values when not all sequences have the same length. If the function is None, return a list of the items of the sequence (or a list of tuples if more than one sequence). """ return []# 两个参数，一个处理函数，一个可迭代的序列# 返回一个列表# 例如计算1到10的平方，并以列表的形式返回map(lambda x: x**2, range(1, 11)）# 结果如下[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]# 当然也可以如下这样使用def square(x): return x**2map(square, range(1, 11))3.reduce() def reduce(function, sequence, initial=None): # real signature unknown; restored from __doc__ """ reduce(function, sequence[, initial]) -> value Apply a function of two arguments cumulatively to the items of a sequence, from left to right, so as to reduce the sequence to a single value. For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates ((((1+2)+3)+4)+5). If initial is present, it is placed before the items of the sequence in the calculation, and serves as a default when the sequence is empty. """ pass# 两个参数，一个接受两个参数的函数，一个序列参数# 例如计算 1到10 的和reduce(lambda x, y: x+y, range(1, 11)）# 当然，不适用lambda匿名函数也可以def add(x, y): return x+yreduce(add, range(1, 11)）# 结果如下454.filter() def filter(function_or_none, sequence): # known special case of filter """ filter(function or None, sequence) -> list, tuple, or string Return those items of sequence for which function(item) is true. If function is None, return the items that are true. If sequence is a tuple or string, return the same type, else return a list. """ pass# 接受两个参数，一个过滤函数，返回True 或者 False ，以及一个序列# 例如，计算100以内的偶数filter(lambda x: x % 2 == 0, range(100)）# 如上def div2(x): if x % 2 == 0: return True else: return Falsefilter(div2, range(100)）# 结果如下 [0, 2, 4, 6, 8, 10, 12, 14, 16,。] 。

文章插图