Using a nested loop to create a nested list

Question

The larger scope of what I am trying to accomplish is this. I have a Windows directory that can contain a variable number of .csv files. These files were generated as test results from a PLC. They are differentiated by their filenames. Every cycle the test generates 2 .csv files. The first file name contains an order number, a - delimiter, and the string UP. The second file is identical except the string is replaced with DOWN.

Example file name:
1234567890-UP or 1234567890-DOWN

Example of directory:
1234567890-UP.csv
1234567890-DOWN.csv
2000005001-UP.csv
2000005001-DOWN.csv

I am trying to write a script that loops through all the file names in the directory and stores them in a list. Then removes everything except the order number from the elements. Then removes duplicate elements. Using the example directory above I would have a list that looks like [1234567890,2000005001]. I have accomplished this much.

Now what I am trying to do is loop through the original list of filenames and compare them against my new list to create a nested list which separates the files based of their order numbers. Using the same example directory the list would look like this: [[1234567890-UP.csv,1234567890-DOWN.csv],[2000005001-UP.csv,2000005001-DOWN.csv]]

Finally I want to loop through this list and merge the .csv files together based off list index.

There might be an easier way to do this that I overlooked that would save me a lot of trouble.

My current code to fill the nested list using a nested for loop looks like this

    nestedlist=[]
    for x in range(len(filenamelist)):
        for y in range(len(filteredlist)):
            if filteredlist[y] in filenamelist[x]:
                nestedlist[y].append(filenamelist[x]

This returns an error Index out of range. This makes since because the size of nestedlist was never defined. I'm not really sure how to do that or what the best way to do that is?

so you want to iterate over the initial list and create a new nested list which is paired?? — Rahul
– Rahul, Commented Jul 3, 2020 at 3:40

leoOrion · Accepted Answer · 2020-07-08 18:23:04Z

1

This could be achieved in a much simpler way. Suppose you have the list of files of the directory as -

files = [1234567890-UP.csv,1234567890-DOWN.csv,2000005001-UP.csv,2000005001-DOWN.csv]

You could iterate over this, create a map of order number to the actual filenames.

filemap = {}
for file in files:
  order_number = re.compile('(\d*)-(\w*).csv').match(file).groups()[0]
  print(order_number)
  files = filemap.get(order_number, [])
  files.append(file)
  filemap[order_number] = files

That should give something like this.

{'1234567890': ['1234567890-UP.csv', '1234567890-DOWN.csv'],
 '2000005001': ['2000005001-UP.csv', '2000005001-DOWN.csv']}

Now you can lookup on the order number and merge when required

edited Jul 8, 2020 at 18:23

answered Jul 3, 2020 at 4:00

leoOrion

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1 Comment

Joey Over a year ago

This solved my problem. Also gave me the opportunity to learn about regular expressions. Thanks!

Signum Ignitum · Accepted Answer · 2020-07-03 03:32:15Z

0

You should append straight to nestedlist, not to nestedlist[y]. There's no index y in an empty list.

You could also simplify this way; the range is unnecessary since you can just loop over the list directly:

nestedlist=[]
   for x in filenamelist:
      for y in filteredlist:
         if y in x:
            nestedlist.append(x)

answered Jul 3, 2020 at 3:32

Signum Ignitum

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