Python Forum

I have a CSV file (A.csv) has many columns. The question is how to modify and save a column in this file and database (data.db). I would like to replace the value 1 in column y based on the previous value:

Output:
A = [ d   x    y    z
      0   1    2    5
      1   2    1    9
      2   8    1    2
      3   3    40   7
      4   6    1    7
      5   4    30   3]

The expected answer should be :

Output:
A = [ d   x    y    z
      0   1    2    5
      1   2    2    9
      2   8    2    2
      3   3    40   7
      4   6    40   7
      5   4    30   3]

import csv
import numpy as np
import numpy
import pandas as pd

conn = sqlite3.connect('data.db')
conn.text_factory = str 
cur = conn.cursor()
A = cur.execute("SELECT * FROM CH1_data")
data = cur.execute('UPDATE CH2_data t1 SET y = (SELECT t2.y FROM CH2_data t2 WHERE t2.d < t1.d AND t2.y <> 1 ORDER BY t2.d DESC LIMIT 1) WHERE y = "" ')

conn.commit()


with open('output_data1001.csv', 'w') as f: 
  writer = csv.writer(f)
  writer.writerow(['d', 'x','y','z'])
  writer.writerows(A)

It does not work. Please help me.......

any help guys?!

Your question is very very jumbled. The root of it is (as was mentioned on SO) that your SQL syntax is wrong - you probably need to learn SQL. You should remove Python from the equation and just use a shell to interact with the database until you're comfortable with it, then you can add the additional complexity of Python.