Pythonic方法修改列表中包含特定数字(不仅仅是字符)的元素

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我正在编写一个函数'简化'来简化多项式,以便simplify("2xy-yx")可以返回"xy"simplify("-a+5ab+3a-c-2a")可以返回"-c+5ab"等等。

我处于合并相同单项式的阶段,但某些单项式的系数为+1-1。我想把它们改成只是+或者-。但我不能直接删除1否则系数值+12-18将分别更改为+2-8

例如

input = '3xy+y-2x+2xy'

到目前为止,我得到了反馈:

Var = ['xy', 'y', 'x']
Coe = ['+5', '+1', '-2']

然后我得到了一个中间结果: IR = ['+5xy', '+1y', '-2x']

我目前的解决方案

[(e[0]+e[2:]) if (e[1]== '1' and e[2].isalpha() ) else e for e in IR ]

它似乎现在执行我要的,但就是看起来很笨重。我想知道是否有更清晰,更简洁的方法来实现同样的目标。最好不要使用正则表达式。

谢谢。

我对此问题的代码如下,还在努力调试

def simplify(poly):

    #If the first coefficient is positive, then I add a + for calculation later on
    if poly[0] !='-':
        poly = '+'+poly
    L = list(poly)

    #Put each monomial in a list as an element
    Temp, e = [], ''
    for i in L:
        if i != '+' and i != '-':
            e += i
        else:
            Temp.append(e)
            e = ''
            e += i

    #The last one will be left out and the first one will be None
    Temp.append(e)
    Temp.pop(0)

    #If the monomial only has a + or - in front of it, then give it a '1' so it's easier for calculation
    SortAndGiveOne = [''.join(e[0] + '1' + e[1:]) if not e[1].isdigit() else e for e in Temp]

    #Try to get letters from each element of the list
    Var = [''.join(sorted(i for i in e if i.isalpha())) for e in SortAndGiveOne]
    #Try to get coefficients from each element of the list
    Coe = [''.join(i for i in e if not i.isalpha()) for e in SortAndGiveOne]

    #Calculation of equivalent monomials
    newvar = []
    newcoe = []
    for va, co in zip(Var, Coe):
        try:
            ind = newvar.index(va)
            newcoe[ind] = str(int(newcoe[ind]) + int(co))
        except ValueError:
            newvar.append(va)
            newcoe.append(co)

    # Put the new lists together
    Put_t = list(map(lambda x,y : y + x, newvar, newcoe))

    # Add the plus sign as it will be gone if there was calculation involved.
    FinalSign = ['+'+ e if e[0] != '+' and e[0] != '-' else e for e in Put_t]

    #Delete the elements with 0 as coefficient
    Delete0 = [e for e in FinalSign if not e[1]=='0']

    #Change the +1 and -1 coefficients to + and - 
    Change1 = [(e[0]+e[2:]) if (e[1]== '1' and e[2].isalpha() ) else e for e in Delete0 ]

    #Sort the list based on length and then lexi order
    FS_sort = sorted(Change1, key = lambda s: (len(''.join(filter(str.isalpha, s))), (''.join(filter(str.isalpha, s)))))

    #Join together as a list
    JT = ''.join(FS_sort)

    #Delete leading plus sign
    if JT[0] == '+':
        JT = JT[1:]

    return JT
提问于
用户回答回答于

看起来你只是想修改['5xy', '+1y', '-2x']['5xy', '+y', '-2x']等等。在这种情况下,我会使用正则表达式:

import re
newlist = [re.sub('(?<=[+-])1(?=[A-Za-z])', '', e) for e in your_list]

测试:

k = ['5xy', '+1y', '-2x', '-1xy', '+11xy']
newlist = [re.sub('(?<=^[+-])1(?=[A-Za-z])', '', e) for e in k]
>>> newlist
['5xy', '+y', '-2x', '-xy', '+11xy']

不过,这看起来并不比你的解决方案好多少。

用户回答回答于

假设可能存在超过两位数的数字,则代码会出错,例如:

IR = ['5xy', '51y', '-2x']
result = [(e[0]+e[2:]) if (e[1]== '1' and e[2].isalpha() ) else e for e in IR ]
print(result)

返回值:

['5xy', '5y', '-2x']

或许更pythonic的方式是使用函数:

def transform(e):
    multiplier = ''.join(c for c in e if c.isnumeric())
    return e[0] + e[2:] if multiplier == '1' else e


IR = ['5xy', '51y', '-2x']
result = [transform(e) for e in IR]
print(result)

IR = ['5xy', '+1y', '-2x']
result = [transform(e) for e in IR]
print(result)

输出:

['5xy', '51y', '-2x']
['5xy', '+y', '-2x']

请注意,转换假定数字是整数,但可以轻松修改以包含浮点数(只需包括检查.)。

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