Using concat for a dictionary I get the error: first argument must be an iterable of pandas objects, you passed an object of type “DataFrame”

Question

I have a dictionary with dataframes, that looks like this:

dataframes = {'Df_20100101': DataFrame, 'Df_20100102': DataFrame, 'Df_20100103': DataFrame}

All dataframes have the same variables (Price, Volume and Date) and the same Index. I want to put all the different dataframes into 1 dataframe. I use the following code:

df = pd.concat([pd.concat(v,ignore_index=True) for k,v in dataframes.items()])

However, I get an error: the first argument must be iterable of pandas objects, you passed an object of type "DataFrame" .

Is it because all the variables have the same Index?

Can anyone help me out?

Thank you!

Answer 1

You're calling pd.concat on individual dataframes in your dictionary (you have nested pd.concat() calls). Instead, you just want a list comprehension to gather the dataframes into a single list and call .concat() on that:

df = pd.concat([v for _, v in dataframes.items()], ignore_index=True)

for k, v is perfectly valid too, but it's customary to use _ for values that you're going to throw away, and you don't use the key here.

You could also just use .values() :

df = pd.concat(dataframes.values(), ignore_index=True)