pandas ValueError:长度不匹配:预期轴有 6 个元素,新值有 1 个元素
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ValueError: Length mismatch: Expected axis has 6 elements, new values have 1 elements
提问by liv2hak
import requests
from bs4 import BeautifulSoup
import pandas as pd
import matplotlib.pyplot as plt
plt.style.use('ggplot')
url = "https://www.google.com/finance/historical?cid=207437&startdate=Jan%201%2C%201971&enddate=Jul%201%2C%202017&start={0}&num=30"
how_many_pages=3
start=0
for i in range(how_many_pages):
new_url = url.format(start)
page = requests.get(new_url)
soup = BeautifulSoup(page.content, "lxml")
table = soup.find_all('table', class_='gf-table historical_price')[0]
columns_header = [th.getText() for th in table.findAll('tr')[0].findAll('th')]
data_rows=table.findAll('tr')[1:]
data=[[td.getText() for td in data_rows[i].findAll(['td'])] for i in range(len(data_rows))]
if start == 0:
final_df = pd.DataFrame(data, columns=columns_header)
else:
df = pd.DataFrame(data, columns=columns_header)
final_df = pd.concat([final_df, df],axis=0)
start += 30
final_df.to_csv('nse_data.csv', sep='\t', encoding='utf-8')
final_df.columns = ['Date']
final_df['Date'] = pd.to_datetime(df['Date'], format='%Y-%m-%d', utc=True)
df.plot(x='Date', y='Close')
plt.savefig('foo.png')
The data downloaded is in the following format
下载的数据格式如下
"Date
" "Open
" "High
" "Low
" "Close
" "Volume
"
0 "Jun 30, 2017
" "9,478.50
" "9,535.80
" "9,448.75
" "9,520.90
" "-
"
1 "Jun 29, 2017
" "9,522.95
" "9,575.80
" "9,493.80
" "9,504.10
" "-
For the time being I only want to plot Date
(on X-axis) against Close
(on Y-axis)
目前我只想绘制Date
(在 X 轴上)对Close
(在 Y 轴上)
However I am getting the error
但是我收到错误
ValueError: Length mismatch: Expected axis has 6 elements, new values have 1 elements
ValueError: Length mismatch: Expected axis has 6 elements, new values have 1 elements
回答by sim0ne
Your headers and data contain newline characters.
print(final_df.columns)
returns:Index(['Date\n', 'Open\n', 'High\n', 'Low\n', 'Close\n', 'Volume\n'], dtype='object')
Use
rstrip
to get rid of them:columns_header = [th.getText().rstrip() for th in table.findAll('tr')[0].findAll('th')]
and
data = [[td.getText().rstrip() for td in data_rows[i].findAll(['td'])] for i in range(len(data_rows))]
final_df.columns = ['Date']
produces your error. A dataframe requires as many headers as its number of columns. Therefore, in your case a list of 6 elements is expected. I'm not sure what you want to do here, I think you can simply remove this line.The format you specify for date parsing does not match your data
['Apr 4, 2017', 'Apr 5, 2017', 'Apr 6, 2017',...]
. Documentation on format codes here. Use instead:final_df['Date'] = pd.to_datetime(df['Date'], format='%b %d, %Y')
Convert your data to numeric values so you can plot them:
final_df['Close'] = [float(val.replace(',', '')) for val in final_df['Close']]
Finally you can call:
final_df.plot(x='Date', y='Close')
您的标题和数据包含换行符。
print(final_df.columns)
返回:Index(['Date\n', 'Open\n', 'High\n', 'Low\n', 'Close\n', 'Volume\n'], dtype='object')
用于
rstrip
摆脱它们:columns_header = [th.getText().rstrip() for th in table.findAll('tr')[0].findAll('th')]
和
data = [[td.getText().rstrip() for td in data_rows[i].findAll(['td'])] for i in range(len(data_rows))]
final_df.columns = ['Date']
产生你的错误。数据框需要与其列数一样多的标题。因此,在您的情况下,预计会有 6 个元素的列表。我不确定你想在这里做什么,我想你可以简单地删除这一行。您为日期解析指定的格式与您的数据不匹配
['Apr 4, 2017', 'Apr 5, 2017', 'Apr 6, 2017',...]
。此处提供有关格式代码的文档。改用:final_df['Date'] = pd.to_datetime(df['Date'], format='%b %d, %Y')
将您的数据转换为数值,以便您可以绘制它们:
final_df['Close'] = [float(val.replace(',', '')) for val in final_df['Close']]
最后你可以调用:
final_df.plot(x='Date', y='Close')