Running a Regex loop in a Pandas Dataframe
<p>I currently have a date column that has some issues. I have attempted to fix the problem but cannot come to a conclusion.</p>

<p>Here is the data:</p>

<pre><code># Import data
df_views = pd.read_excel('PageViews.xlsx')

# Check data types
df_views.dtypes
Out[57]:
Date           object
Customer ID     int64
dtype: object
</code></pre>

<p>The date column is not in a 'datetime' data format as expected. Further inspection yields:</p>

<pre><code>df_views.ix[:5]
Date    Customer ID
0   01/25/2016  104064596300
1   02/28/2015  102077474472
2   11/17/2016  106430081724
3   02/24/2016  107770391692
4   10/05/2016  106523680888
5   02/24/2016  107057691592
</code></pre>

<p>I quickly check which rows does not follow the proper format xx/xx/xxxx</p>

<pre><code>print (df_views[df_views["Date"].str.len() != 10])
          Date   Customer ID
189513  12/14/  106285770688
189514  10/28/  107520462840
189515  11/01/  102969804360
189516  11/10/  102106417100
189517  02/16/  107810168068
189518  10/25/  102096164504
189519  02/08/  107391760644
189520  02/29/  107353558928
189521  10/24/  107209142140
189522  12/20/  107875461336
189523  12/23/  107736375428
189524  11/12/  106561080372
189525  01/27/  102676548120
189526  11/19/  107733043896
189527  12/31/  107774452412
189528  01/21/  102610956040
189529  01/09/  108052836888
189530  02/21/  106380330112
189531  02/02/  107844459772
189532  12/12/  102006641640
189533  12/16/  106604647688
189534  11/14/  102383102504
</code></pre>

<p>I have attempted to create a for loop but cannot figure out how to approach my loop.</p>

<p>Important note: I know that the time period for all observations is between September 2015 through February 2016.</p>

<p>So if the month is 09/10/11/12 - then I can add "2015" to the date, 
otherwise if the month is 01/02, I can add "2016".</p>

<pre><code>for row in df_views["Date"]:
    if len(row) != 10:
        if row.str.contains("^09|10|11|12\/"):
            row.str.cat("2015")
        elif row.str.contains("^01|02\/"):
            row.str.cat("2016")
    else:
        continue 
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
&lt;ipython-input-87-684e121dd62d&gt; in &lt;module&gt;()
      5 for row in df_views["Date"]:
      6     if len(row) != 10:
----&gt; 7         if row.str.contains("^09|10|11|12\/"):
      8             row.str.cat("2015")
      9         elif row.str.contains("^01|02\/"):

AttributeError: 'str' object has no attribute 'str'
</code></pre>

<p>As <a href="http://stackoverflow.com/questions/39397897/running-a-regex-loop-in-a-pandas-dataframe/39398702#comment66122084_39397897">@BrenBam has already written in the comment</a> - try to avoid using loops. Pandas gives us tons of vectorized (read fast and efficient) methods:</p>

<pre><code>In [67]: df
Out[67]:
          Date   Customer ID
0   12/14/2001  106285770688
1   10/28/2000  107520462840
2       11/01/  102969804360
3       11/10/  102106417100
4       02/16/  107810168068
5       10/25/  102096164504
6       02/08/  107391760644
7       02/29/  107353558928
8       10/24/  107209142140
9       12/20/  107875461336
10      12/23/  107736375428
11      11/12/  106561080372
12      01/27/  102676548120
13      11/19/  107733043896
14      12/31/  107774452412
15      01/21/  102610956040
16      01/09/  108052836888
17      02/21/  106380330112
18      02/02/  107844459772
19      12/12/  102006641640
20      12/16/  106604647688
21      11/14/  102383102504

In [68]: df.ix[df.Date.str.match(r'^(?:09|10|11|12)\/\d{2}\/$', as_indexer=True), 'Date'] += '2015'

In [69]: df.ix[df.Date.str.match(r'^(?:01|02)\/\d{2}\/$', as_indexer=True), 'Date'] += '2016'

In [70]: df
Out[70]:
          Date   Customer ID
0   12/14/2001  106285770688
1   10/28/2000  107520462840
2   11/01/2015  102969804360
3   11/10/2015  102106417100
4   02/16/2016  107810168068
5   10/25/2015  102096164504
6   02/08/2016  107391760644
7   02/29/2016  107353558928
8   10/24/2015  107209142140
9   12/20/2015  107875461336
10  12/23/2015  107736375428
11  11/12/2015  106561080372
12  01/27/2016  102676548120
13  11/19/2015  107733043896
14  12/31/2015  107774452412
15  01/21/2016  102610956040
16  01/09/2016  108052836888
17  02/21/2016  106380330112
18  02/02/2016  107844459772
19  12/12/2015  102006641640
20  12/16/2015  106604647688
21  11/14/2015  102383102504
</code></pre>

python regex loops pandas numpy