Dataframe returning empty after assignment of values?

Question

Essentially, I would like to add values to certain columns in an empty DataFrame with defined columns, but when I run the code, I get.

Empty DataFrame
Columns: [AP, AV]
Index: []

Code:

df = pd.DataFrame(columns=['AP', 'AV'])  
df['AP'] = propName 
df['AV'] = propVal

I think this could be a simple fix, but I've tried some different solutions to no avail. I've tried adding the values to an existing dataframe I have, and it works when I do that, but would like to have these values in a new, separate structure.

Thank you,

@G.Anderson PropName and propVal are values pulled from a DataFrame I'm reading in from Excel called propData: propName = propData.iloc[1, 0] idx = propData.index[propData[0] == 'Total Unleveraged Present Value'].tolist()[0] propVal = propData.iloc[idx, 1] — Akashdas221
– Akashdas221, Commented Apr 19, 2022 at 17:34
Updated my message with a detailed description of the reason. — inquirer
– inquirer, Commented May 1, 2022 at 11:40

inquirer · Accepted Answer · 2022-05-01 11:39:26Z

2

It's the lack of an index. If you create an empty dataframe with an index.

df = pd.DataFrame(index = [5])

Output

Empty DataFrame
Columns: []
Index: [5]

Then when you set the value, it will be set.

df[5] = 12345

Output

       5
5  12345

You can also create an empty dataframe. And when setting a column with a value, pass the value in the list. The index will be automatically set.

df = pd.DataFrame()
df['qwe'] = [777]

Output

   qwe
0  777

edited May 1, 2022 at 11:39

answered Apr 19, 2022 at 17:37

inquirer

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5 Comments

Akashdas221 Over a year ago

I need to define the DataFrame to use globally. propName and propValue are local variables used within a for-loop. Any tips?

inquirer Over a year ago

Initialize with some specific values, and then replace them with the necessary ones. If you have a pre-known number of values for columns?

Akashdas221 Over a year ago

Thanks, that works! Can you explain why your code works, but mine didn't? New to this and want to learn.

inquirer Over a year ago

As far as I understand, an empty dataframe has no) index

Akashdas221 Over a year ago

Understood, but I thought me assigning a value would no longer make the dataframe empty? For example, I initialize another empty dataframe, and then populate that dataframe with data from yet another dataframe, and that works with no issues.

Akashdas221 · Accepted Answer · 2022-04-20 15:47:34Z

0

Assign propName and propValue to dictionary:

dict = {}
dict[propName] = propValue

Then, push to empty DataFrame, df:

df = pd.DataFrame()
df['AP'] = dict.keys()
df['AV'] = dict.values()

Probably not the most elegant solution, but works great for me.

answered Apr 20, 2022 at 15:47

Akashdas221

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