格式化CSV文件

Question

I have a csv file with no formatting. I need to format the csv file.

import pandas
df = pandas.read_csv('abc.csv')
df['speed'] = df['speed'].map('{:06,.2f}'.format)
df.to_csv("FINAL.csv")

Error:

Traceback (most recent call last):
File "<stdin>", line 3, in <module>
File "C:\Python27\ArcGIS10.4\lib\site-packages\pandas\core\series.py", line 2009, in map
mapped = map_f(values, arg)
File "pandas\src\inference.pyx", line 1064, in pandas.lib.map_infer (pandas\lib.c:58525)
ValueError: Unknown format code 'f' for object of type 'str'

For Example:

df['speed'] = [54,156,3]

Expected output:

speed
054.00
156.00
003.00

Answer 1

Remove the comma in your string formatting and it should work.

import pandas as pd
df = pd.DataFrame([54,156,3])
df[0].map('{:06.2f}'.format)

output:

054.00
156.00
003.00

Here's a reasource for string formatting:

https://pyformat.info/

Edit:
It sounds like this is a problem of messy data. I suggest trying the following options when reading your csv file:

df = pandas.read_csv('abc.csv', dtype=object)
df['speed'] = df['speed'].apply(pd.to_numeric, errors='coerce')
df['speed'] = df['speed'].map('{:06.2f}'.format)

errors='coerce' will try to convert to float, and return NaN if it fails to do so.