从Python中的元组列表中查找相等的值

Question

经过大量搜索没有成功,我需要帮助.

我有一个元组列表列表.列表列表中的每个列表代表我系统中的特定数量的公式.此列表中的任何元素都是一个元组,表示元素的类型(变量,参数,常量,操作...)和元素的名称.例如,对于公式x1 + x2 + A1,x1-x3和sin(x2)+ A1,我们将:

[
[('VAR', 'x1'), ('PLUS', '+'), ('VAR', 'x2'), ('PLUS', '+'), ('PAR', 'A1')],
[('VAR', 'x1'), ('LESS', '-'), ('VAR', 'x3')],
[('SIN', 'sin'), ('VAR', 'x2'), ('PLUS', '+'), ('PAR', 'A1')]
]

我正在尝试确定每个变量出现在哪个公式中.在上面的例子中,我认为x1变量是1和2公式,x2变量是1和3公式,x3是2公式,所以我的输出将是这样的:

[
['x1', 1, 2],
['x2', 1, 3],
['x3', 2],
]

目前我的代码非常低效,根本不起作用,但这里是:

cont = 0
for subL1 in L:
    for subL2 in L:
        if len(subL1) != 1 and len(subL2) != 1:
            if subL1 != subL2 and subL2:
                for x,y in subL1:
                    for z,t in subL2:
                        if (    x == 'VAR'
                            and z == 'VAR'
                            and y == t
                            ):
                            print "Variable", y , "repeated"
        else:
            print "list with 1 lenght\n"
    subL1.pop(0)
cont = cont + 1

Answer 1

您可以使用a collections.defaultdict来存储每个变量的公式(实际上是列表列表中的索引):

from collections import defaultdict

dd = defaultdict(set)              # use a set as factory so we don't keep duplicates
for idx, subl in enumerate(l, 1):  # iterate over the sublists with index starting at 1
    for subt in subl:              # iterate over each tuple in each sublist
        label, val = subt          # unpack the tuple
        if label == 'VAR':         # if it's a VAR save the index in the defaultdict
            dd[val].add(idx)

例如:

l = [[('VAR', 'x1'), ('PLUS', '+'), ('VAR', 'x2'), ('PLUS', '+'), ('PAR', 'A1')],
     [('VAR', 'x1'), ('LESS', '-'), ('VAR', 'x3')],
     [('SIN', 'sin'), ('VAR', 'x2'), ('PLUS', '+'), ('PAR', 'A1')]
    ]

它给:

print(dd)
# defaultdict(set, {'x1': {1, 2}, 'x2': {1, 3}, 'x3': {2}})

要获得所需的输出,您只需将其再次转换为列表,例如(仅限python-3.x):

>>> [[name, *sorted(formulas)] for name, formulas in sorted(dd.items())]
[['x1', 1, 2], ['x2', 1, 3], ['x3', 2]]

Answer 2

formula = [
[('VAR', 'x1'), ('PLUS', '+'), ('VAR', 'x2'), ('PLUS', '+'), ('PAR', 'A1')],
[('VAR', 'x1'), ('LESS', '-'), ('VAR', 'x3')],
[('SIN', 'sin'), ('VAR', 'x2'), ('PLUS', '+'), ('PAR', 'A1')]
]

variables = collections.defaultdict(set)
for line_no, line in enumerate(formula):
    for typ, value in line:
        if typ == 'VAR':
            variables[value].add(line_no)

variables

defaultdict(set,{'x1':{0,1},'x2':{0,2},'x3':{1}})