我正在写一个' simplify‘函数来简化多项式,这样simplify("2xy-yx")
就可以返回"xy"
,simplify("-a+5ab+3a-c-2a")
就可以返回"-c+5ab"
,依此类推。
在这个阶段,我合并了相同的单项式,但某些单项式的系数将为+1
或-1
。我想只将它们更改为+
或-
。但我不能直接删除1,否则值为+12
或-18
的系数将分别更改为+2
和-8
。
例如
input = '3xy+y-2x+2xy'
到目前为止,我的流程给了我:
Var = ['xy', 'y', 'x']
Coe = ['+5', '+1', '-2']
然后我得到了一个中间结果:IR = ['+5xy', '+1y', '-2x']
我目前的解决方案是:
[(e[0]+e[2:]) if (e[1]== '1' and e[2].isalpha() ) else e for e in IR ]
它现在似乎为我做了这项工作,但看起来很笨拙。我想知道是否有更干净、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。
编辑:我为这个问题编写的代码。我还在调试它。
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
发布于 2018-12-05 04:17:21
看起来您只想将['5xy', '+1y', '-2x']
修改为['5xy', '+y', '-2x']
等。在本例中,我将使用正则表达式:
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,这看起来并不比您的解决方案好多少。
https://stackoverflow.com/questions/53620531
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