Pandas to_datetime: Unknown string format

Question

The 'Date' column in the dataframe is like this:

19 Mar. 2017
12 Mar. 2017
08 Mar. 2017
05 Mar. 2017
26 Feb. 2017
19 Feb. 2017
12 Feb. 2017
05 Feb. 2017
29 Jan. 2017
22 Jan. 2017
15 Jan. 2017
08 Jan. 2017
01 Jan. 2017
25 Dec. 2016
18 Dec. 2016
11 Dec. 2016
04 Dec. 2016
27 Nov. 2016
20 Nov. 2016

When I tried to do：

df = df[pd.to_datetime(df['Date']).dt.year==2016]

It complained:

ValueError: Unknown string format

I think it cannot recognize the date string format.

Any idea how to solve this？

jpp · Accepted Answer · 2018-09-25 13:10:46Z

2

You can specify format with pd.to_datetime for non-standard formats, e.g. pd.to_datetime(my_series, format='%d %b. %Y'). Then use pd.Series.dt.year. This is the recommended method. See also Python's strftime directives.

However, if you are only converting to datetime to filter by year and not changing the dtype of your series, you can just query the last 4 characters:

df[df['dates'].str[-4:] == '2016']

answered Sep 25, 2018 at 13:10

jpp

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Comments

jezrael · Accepted Answer · 2018-09-25 13:06:06Z

1

Use custom format by parameter format in to_datetime:

df['Date'] = pd.to_datetime(df['Date'], format='%d %b. %Y')
df = df[df['Date'].dt.year==2016]
print (df)
         Date
13 2016-12-25
14 2016-12-18
15 2016-12-11
16 2016-12-04
17 2016-11-27
18 2016-11-20

answered Sep 25, 2018 at 13:06

jezrael

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1 Comment

Chan Austin Over a year ago

there are two sorts of formats in the 'Date' column:27 Nov. 2016 and 28 May 2018

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