I have a dynamic DataFrame which works fine, but when there are no data to be added into the DataFrame I get an error. And therefore I need a solution to create an empty DataFrame with only the column names.
For now I have something like this:
df = pd.DataFrame(columns=COLUMN_NAMES) # Note that there are now row data inserted. PS: It is important that the column names would still appear in a DataFrame.
But when I use it like this I get something like that as a result:
Index([], dtype='object') Empty DataFrame The "Empty DataFrame" part is good! But instead of the Index thing I need to still display the columns.
Edit:
An important thing that I found out: I am converting this DataFrame to a PDF using Jinja2, so therefore I'm calling out a method to first output it to HTML like that:
df.to_html() This is where the columns get lost I think.
Edit2: In general, I followed this example: . The css is also from the link. That's what I do to send the dataframe to the PDF:
env = Environment(loader=FileSystemLoader('.')) template = env.get_template("pdf_report_template.html") template_vars = {"my_dataframe": df.to_html()} html_out = template.render(template_vars) HTML(string=html_out).write_pdf("my_pdf.pdf", stylesheets=["pdf_report_style.css"]) Edit3:
If I print out the dataframe right after creation I get the followin:
[0 rows x 9 columns] Empty DataFrame Columns: [column_a, column_b, column_c, column_d, column_e, column_f, column_g, column_h, column_i] Index: [] That seems reasonable, but if I print out the template_vars:
'my_dataframe': '<table border="1">\n <tbody>\n <tr>\n <td>Index([], dtype=\'object\')</td>\n <td>Empty DataFrame</td>\n </tr>\n </tbody>\n</table>' And it seems that the columns are missing already.
E4: If I print out the following:
print(df.to_html()) I get the following result already:
<table border="1"> <tbody> <tr> <td>Index([], dtype='object')</td> <td>Empty DataFrame</td> </tr> </tbody> </table> 4 Answers
You can create an empty DataFrame with either column names or an Index:
In [4]: import pandas as pd In [5]: df = pd.DataFrame(columns=['A','B','C','D','E','F','G']) In [6]: df Out[6]: Empty DataFrame Columns: [A, B, C, D, E, F, G] Index: [] Or
In [7]: df = pd.DataFrame(index=range(1,10)) In [8]: df Out[8]: Empty DataFrame Columns: [] Index: [1, 2, 3, 4, 5, 6, 7, 8, 9] Edit: Even after your amendment with the .to_html, I can't reproduce. This:
df = pd.DataFrame(columns=['A','B','C','D','E','F','G']) df.to_html('test.html') Produces:
<table border="1"> <thead> <tr> <th></th> <th>A</th> <th>B</th> <th>C</th> <th>D</th> <th>E</th> <th>F</th> <th>G</th> </tr> </thead> <tbody> </tbody> </table> Are you looking for something like this?
COLUMN_NAMES=['A','B','C','D','E','F','G'] df = pd.DataFrame(columns=COLUMN_NAMES) df.columns Index(['A', 'B', 'C', 'D', 'E', 'F', 'G'], dtype='object') Creating colnames with iterating
df = pd.DataFrame(columns=['colname_' + str(i) for i in range(5)]) print(df) # Empty DataFrame # Columns: [colname_0, colname_1, colname_2, colname_3, colname_4] # Index: [] to_html() operations
print(df.to_html()) # <table border="1"> # <thead> # <tr> # <th></th> # <th>colname_0</th> # <th>colname_1</th> # <th>colname_2</th> # <th>colname_3</th> # <th>colname_4</th> # </tr> # </thead> # <tbody> # </tbody> # </table> this seems working
print(type(df.to_html())) # <class 'str'> The problem is caused by
when you create df like this
df = pd.DataFrame(columns=COLUMN_NAMES) it has 0 rows × n columns, you need to create at least one row index by
df = pd.DataFrame(columns=COLUMN_NAMES, index=[0]) now it has 1 rows × n columns. You are be able to add data. Otherwise its df that only consist colnames object(like a string list).
df.to_html() has a columns parameter.
Just pass the columns into the to_html() method.
df.to_html(columns=['A','B','C','D','E','F','G']) 
