Trying to concatenate dataframes with numpy and recursion-CodePudding

I have a list of pandas dataframes, which I am trying to concatenate into one dataframe using recursion and numpy.

def recur(framelist, index=0, result=0):


    if index == len(framelist)-1:
        return result

    else:
        return recur(np.concatenate((framelist[index],framelist[index 1])))

My intention with the above is to pass the dataframe list to the recur function. The base case is when the end of the list is reached. the functionality is to concat all pairs of dataframes

However I get an error that 0 dimensional arrays cannot be concatenated

CodePudding user response：

To work out what's going on it's a good idea to walk through it step by step.

You say your initial call to recur passes in a list of panda dataframes. You don't show the creation of them, but let's say they're something like...

framelist = [
    pd.DataFrame(np.array([1, 2, 3])),
    pd.DataFrame(np.array([4, 5])),
    pd.DataFrame(np.array([6, 7])),
    pd.DataFrame(np.array([8]))
    ]

So, first time through it concatenates the first two entries from framelist as numpy arrays.

[[1], [2],  [3]]  and [[4], [5]]

This will result in a numpy ndarray which looks like:

[[1], [2], [3], [4], [5]]

This result is passed into recur() as the new framelist

Second time through it concatenates the first two entries from framelist.

[1] and [2]

This will result in a numpy array which looks like:

[1, 2]

This result is passed into recur() as the new framelist

Third time through it concatenates the first two entries from framelist.

1 and 2

These are simply numbers, not arrays, so you see the error '0 dimensional arrays cannot be concatenated'