read csv files in python

问题

I need to read one column from the multiple csv file present in folder and then extract minimum and maximum dates from the column.

For e.g. if i have folder path "/usr/abc/xyz/" and multiple csv files are present as below

aaa.csv
bbb.csv
ccc.csv

and the files are containing data

aaa.csv is containing the data

name,address,dates
xxx,11111,20190101
yyy,22222,20190201
zzz,33333,20190101

bbb.csv is containing the data

name,address,dates
fff,11111,20190301
ggg,22222,20190501
hhh,33333,20190601

so I need to extract the minimum and maximum dates from the files and in the above case the date range should be 20190101 to 20190601

Can anyone please help how can i extract the minimum and maximum dates from the files in python

I need to avoid pandas or any other package as I need to read csv files in directly in pyhton

回答1:

import pandas as pd

dt = pd.read_csv('you_csv.csv')
print(max(dt['dates']))
print(min(dt['dates']))

If you need to avoid pandas you can do the following which is not recommended at all:

dt = []
with open('your_csv.csv', 'r') as f:
    data = f.readlines()
for row in data:
    dt.append(row.split(',')[2].rstrip())
dt.pop(0)
print(max(dt))
print(min(dt))

回答2:

A solution only using the available core libraries. It doesn't read the whole file into memory so should have a very low footprint and will work with larger files.

pathlib is used to get all the csv files
datetime is used to convert to dates
sys is used for user input

$ python3 date_min_max.py /usr/abc/xyz/
min date: 2019-01-01 00:00:00
max date: 2019-06-01 00:00:00

date_min_max.py

from pathlib import Path
from datetime import datetime
import sys


if len(sys.argv) > 1:
    p = sys.argv[1]
else:
    p = "."

files = [x for x in Path(p).iterdir() if x.suffix == ".csv"]

date_format = "%Y%m%d"

dt_max = datetime.strptime("19000101", date_format)
dt_min = datetime.strptime("30000101", date_format)
for file in files:
    with file.open("r") as fh:
        for i, line in enumerate(fh):
            if i == 0:
                continue
            t = line.strip().split(",")[2]
            dt_max = max(dt_max, datetime.strptime(t, date_format))
            dt_min = min(dt_min, datetime.strptime(t, date_format))


print("min date: {}\nmax date: {}".format(dt_min, dt_max))

来源：https://stackoverflow.com/questions/57956289/read-csv-files-in-python

标签

python

csv