在Python中创建和排序2D列表

Question

I am new to Python. I need to traverse the list of files in a directory, and have a 2D list of files (keys) with a value. Then I need to sort it based on their values, and delete the files with lower half of values. How can I do that?

This is what I did so far. I can't figure it out how to create such 2D array.

dir = "images"
num_files=len(os.listdir(dir))
for file in os.listdir(dir):
    print(file)
    value = my_function(file)
    #this is wrong:
    _list[0][0].append(value)

#and then sorting, and removing the files associated with lower half

Basically, the 2D array should look like [[file1, 0.876], [file2, 0.5], [file3, 1.24]] , which needed to be sorted out based on second indexes.

Answer 1

Based on the comments, looks like I have to do this when appending:

mylist.append([file, value])

And for sorting, I have to do this:

mylist.sort(key=lambda mylist: mylist[1])

Answer 2

I don't understand what this message means.

delete the files with lower half of values

Does this mean that you have to select the files having value less than the midpoint between minimum and maximum values on the files or that you just have to select the lower half of the files?

There isn't any need to use a 2D-array if the second coordinate depends on the first thanks to my_function . Here is a function that does what you need:

from os import listdir as ls
from os import remove as rm
from os.path import realpath

def delete_low_score_files(dir, func, criterion="midpoint")
    """Delete files having low score according to function f

       Args:
           dir (str): path of the dir;
           func (fun): function that score the files;
           criterion (str): can be "midpoint" or "half-list";
       Returns:
           (list) deleted files.
    """

    files = ls(dir)
    sorted_files = sorted(files, key=func)    

    if criterion == "midpoint":
        midpoint = func(sorted_files[-1]) - func(sorted_files[0])
        files_to_delete = [f for f in sorted_files if func(f) < midpoint]

    if criterion == "half-list":
        n = len(sorted_files)/2
        files_to_delete = sorted_files[:n]

    for f in files_to_delete:
        rm(realpath(f))

    return files_to_delete