如何将Excel公式应用于整个列中的值？

Question

I am trying to parse file names in a folder and figured out how to load them into a csv file but I need to apply a formula to the column in order to get my final results. The code and data is as follows along with the Excel formula I plan on using.

This snippet of code takes the file names from the folder "testfolder" and dumps them in the csv file.

Code:

import os, csv

f = open("/home/niteninja/Documents/sampledata.csv", 'r+')
w=csv.writer(f)
for path, dirs, files in os.walk("/home/niteninja/testfolder"):
    for filename in files:
        w.writerow([filename])

f.truncate()

This is an example of what the data in the csv file looks like after running the code above.

sampledata.csv:

       A                  B

ndjsmdhfr_145874 

jdmsjfht_273647

hfgryuyw_756475

jgmfhdhr_736453

jdmsdhfyt_548745

What I want to do is implement this formula : "LEFT(A1,FIND("_",A1) - 1)" in column B.

The purpose of this is to eliminate the underscores and any characters that come after it. I want to be able to apply this formula to the cells in column A and output the new values to column B. I am unable to figure out the proper syntax to approach this problem.

Answer 1

First define a function for a single string:

def splitter(x):
    return x.split('_')[0]

print(splitter('ndjsmdhfr_145874'))
# ndjsmdhfr

Then write to your CSV file. Remember to use newline='' as an argument to open . In addition, it's recommended you use the with open(...) construct for reading / writing files. Here's some pseudo-code:

with open('out_file.csv', 'w', newline='') as fout:
    w = csv.writer(fout)
    for path, dirs, files in os.walk("/home/niteninja/testfolder"):
        for filename in files:
            w.writerow([filename, splitter(filename)])

Answer 2

These three lines of code will select the first cell in column B and apply the formula, then copy it down the column

Range("B1").Select
ActiveCell.FormulaR1C1 = "=LEFT(RC[-1],FIND(""_"",RC[-1]) - 1)"
Selection.AutoFill Range(ActiveCell, ActiveCell.Offset(0, -1).End(xlDown).Offset(0, 1))