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Py学习  »  Python

在Python中,仅将新值从DataFrame追加到CSV

Fogarasi Norbert • 5 年前 • 1768 次点击  

Date,High,Low,Open,Close,Volume,Adj Close
1980-12-12,0.515625,0.5133928656578064,0.5133928656578064,0.5133928656578064,117258400.0,0.02300705946981907
1980-12-15,0.4888392984867096,0.4866071343421936,0.4888392984867096,0.4866071343421936,43971200.0,0.02180669829249382
1980-12-16,0.453125,0.4508928656578064,0.453125,0.4508928656578064,26432000.0,0.02020619809627533

我还有一个 Pandas DataFrame 它有完全相同的值,但也有新的条目。我的目标是只将新值追加到CSV文件中。

我试过这样做,但不幸的是,这不仅附加了新条目,还附加了旧条目:

df.to_csv('{}/{}'.format(FOLDER, 'AAPL.CSV'), mode='a', header=False)
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1768 次点击  
文章 [ 1 ]  |  最新文章 5 年前
cullzie
Reply   •   1 楼
cullzie    6 年前

您可以在写入csv文件后重新读取它,并在追加新获取的数据之前删除任何重复的文件。

以下代码对我有效:

import pandas as pd

# Creating original csv
columns = ['Date','High','Low','Open','Close','Volume','Adj Close']
original_rows = [["1980-12-12",0.515625,0.5133928656578064,0.5133928656578064,0.5133928656578064,117258400.0,0.02300705946981907], ["1980-12-15",0.4888392984867096,0.4866071343421936,0.4888392984867096,0.4866071343421936,43971200.0,0.02180669829249382
]]
df_original = pd.DataFrame(columns=columns, data=original_rows)
df_original.to_csv('AAPL.CSV', mode='w', index=False)

# Fetching the new data
rows_updated = [["1980-12-12",0.515625,0.5133928656578064,0.5133928656578064,0.5133928656578064,117258400.0,0.02300705946981907], ["1980-12-15",0.4888392984867096,0.4866071343421936,0.4888392984867096,0.4866071343421936,43971200.0,0.02180669829249382
], ["1980-12-16",0.453125,0.4508928656578064,0.453125,0.4508928656578064,26432000.0,0.02020619809627533]]
df_updated = pd.DataFrame(columns=columns, data=rows_updated)

# Read in current csv values
current_csv_data = pd.read_csv('AAPL.CSV')

# Drop duplicates and append only new data
new_entries = pd.concat([current_csv_data, df_updated]).drop_duplicates(subset='Date', keep=False)
new_entries.to_csv('AAPL.CSV', mode='a', header=False, index=False)