Python: looping through a list at certain indices (containing certain string)-CodePudding

So I want to loop through a list starting at string "B" to the end or until a new "B" is reached and so on till the end of the list.

        l=["A", "B", "C", "D", "B", "M", "C", "T", "B", "g", "do"]
        index = [idx for idx, s in enumerate(l) if 'B' in s]
        print(index)

I want to loop through the list so I get these outputs but without hard coding the indices:

l[1:4]=['B', 'C', 'D']
l[4:8]=['B', 'M', 'C', 'T']
l[8:]=['B', 'g', 'do']

If just one index has that string then

l=["A", "B", "C", "D"]
index = [idx for idx, s in enumerate(l) if 'B' in s]
print(index)
l[1:]=["B", "C", "D"]

CodePudding user response：

Try this:

def get_lists(l):
    indices = [i for i, x in enumerate(l) if x == "B"]
    if len(indices) == 0:
        return []
    elif len(indices) == 1:
        return [[l[indices[0]]]]
    else:
        result = list()
        for i in range(len(indices)):
            if indices[i] == indices[-1]:
                result.append(l[indices[i]:])
            else:
                result.append(l[indices[i]:indices[i 1]])
    
        return result
        
k = ["A", "B", "C", "D", "B", "M", "C", "T", "B", "g", "do"]
print(get_lists(k))

Output:

[['B', 'C', 'D'], ['B', 'M', 'C', 'T'], ['B', 'g', 'do']]

CodePudding user response：

l = ["A", "B", "C", "D", "B", "M", "C", "T", "B", "g", "do"]

#note that an extra 'B' is added to the list: l ['B']
indexOfB = [i for i, x in enumerate(l ['B']) if x == 'B']

Blists = [l[i[0]:i[1]] for i in zip(indexOfB, indexOfB[1:])]

[print(x) for x in Blists]

CodePudding user response：

Taking your code and using a for loop:

l = ["A", "B", "C", "D", "B", "M", "C", "T", "B", "g", "do"]

index = [idx for idx, s in enumerate(l) if 'B' in s]

out_of_bounds_index = len(index)

result = []

for i in range(out_of_bounds_index):
    if i 1 < out_of_bounds_index:
        result.append(l[index[i]:index[i 1]])
    else:
        result.append(l[index[i]:])
        
print(result)

Or a list comprehension:

l = ["A", "B", "C", "D", "B", "M", "C", "T", "B", "g", "do"]

index = [idx for idx, s in enumerate(l) if 'B' in s]

out_of_bounds_index = len(index)

result = [l[index[i]:index[i 1]] 
          if i 1 < out_of_bounds_index 
          else l[index[i]:] 
          for i in range(out_of_bounds_index)]
        
print(result)

Output:

[['B', 'C', 'D'], ['B', 'M', 'C', 'T'], ['B', 'g', 'do']]