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pythonliststring-concatenation

Conditional joining in a list

I have a Python list:

data = ['Cost', '$', 4244, '$', 4090, '$', 3967]

What I want to do is merge the $ with preceding element and obtain a new list:

data = ['Cost', '$4244', '$4090', '$3967']

What is the best way to achieve this?

Solution

  • You could make use of iterators:

    data_iter = iter(data)
[e + str(next(data_iter)) if e == '$' else e for e in data_iter]

    This makes use of the fact we can obtain the next element of an iterable, even while looping over the iterable. Each time a '$' string is found, the next element is pulled in and concatenated as a string.

    Demo:

    >>> data = ['Cost', '$', 4244, '$', 4090, '$', 3967]
>>> data_iter = iter(data)
>>> [e + str(next(data_iter)) if e == '$' else e for e in data_iter]
['Cost', '$4244', '$4090', '$3967']