如何将一个元素与列表中的其他元素进行比较

Question

I have a list x = [a, b, c, d] .

I want to compare:

1. First element a with b , c and d .
2. Second element b with a , c and d .
3. Third element c with a , b and d .
4. Fourth element d with a , b and c .

This is the method I have used but it's not working as I want:

for i in len(x):
    for j in range(i+1, len(x)):
        Compare(x[i], y[j])

Answer 1

for i in range(len(x)):
    for el in x[:i] + x[(i+1):]:
        print("Compare {} with {}".format(x[i], el))
        # or: Compare(x[i], el)
"""
Output:
Compare a with b
Compare a with c
Compare a with d
Compare b with a
Compare b with c
Compare b with d
Compare c with a
Compare c with b
Compare c with d
Compare d with a
Compare d with b
Compare d with c
"""

As a function:

def exclusive_compare(l, comparefun):
    return [comparefun(l[i], el) for el in l[:i] + l[(i+1):] for i in range(len(l))]

exclusive_compare(l, lambda x, y: (x, y))

Out[9]: 
[('a', 'b'),
 ('a', 'c'),
 ('a', 'd'),
 ('b', 'a'),
 ('b', 'c'),
 ('b', 'd'),
 ('c', 'a'),
 ('c', 'b'),
 ('c', 'd'),
 ('d', 'a'),
 ('d', 'b'),
 ('d', 'c')]

Answer 2

This looks like a good place to use itertools .

for i in list(itertools.permutations(x, 2)):
    print("Compare {0} with {1}".format(*i))

"""    
Compare a with b
Compare a with c
Compare a with d
Compare b with a
Compare b with c
Compare b with d
Compare c with a
Compare c with b
Compare c with d
Compare d with a
Compare d with b
Compare d with c
"""

If a == b and b == a then you can use combinations to get distinct pairs:

for i in list(itertools.combinations(x, 2)):
    print("Compare {0} with {1}".format(*i))

"""
Compare a with b
Compare a with c
Compare a with d
Compare b with c
Compare b with d
Compare c with d
"""

Answer 3

A silly mistake, you forgot to print hte comparison. Here is the solution:

For i in len(x):
 For j in range(i+1, len(x)):
  print(Compare(x[i], y[j]))