How to save a list of string in sublists according specific expression?

Question

I\'m doing a script to save a read path in sublist. Let\'s suppose I have 400 file paths saved in a list, every path has the specific syntax Ci_whaterver.csv, then

Answer 1

One way will be to create a dictionary and use the part Ci as key and lists of file names starting with Ci will be the value. For example, take pathlist = ['C1_01.csv','C1_02.csv', 'C2_01.csv' , 'C3_01.csv', 'C2_02.csv'], then we will create a dictionary which will store

{'C1': ['C1_01.csv', 'C1_02.csv'], 'C2': ['C2_01.csv', 'C2_02.csv'], 'C3': ['C3_01.csv']}

Here is the code:

pathlist = ['C1_01.csv','C1_02.csv', 'C2_01.csv' , 'C3_01.csv', 'C2_02.csv']
d = {}
for path in pathlist:
    if path[:2] not in d:
        d[path[:2]] = [path]
    else:
        d[path[:2]].append(path)
pathlistf = []
for key in d:
    pathlistf.append(d[key])
print(pathlistf)
# Output: [['C1_01.csv', 'C1_02.csv'], ['C3_01.csv'], ['C2_01.csv', 'C2_02.csv']]

Hope this solves the problem. Feel free to ask any doubt.

Answer 2

If pathlist is pre-sorted, you can use the following code based on the itertools.groupby.

from itertools import groupby
pathlist=['Cn_01.csv', 'C1_02.csv', 'C9_01.csv', 'C9_02.csv', 'Ca_01.csv', 'C9_03.csv', 'Ca_02.csv', 'C1_01.csv', 'Cn_02.csv']
pathlist.sort()
groupedfilenames = (list(g) for _, g in groupby(pathlist, key=lambda a: a[:2]))
print(list(groupedfilenames))

Output:

[['C1_01.csv', 'C1_02.csv'], ['C9_01.csv', 'C9_02.csv', 'C9_03.csv'], ['Ca_01.csv', 'Ca_02.csv'], ['Cn_01.csv', 'Cn_02.csv']]