Returns a DataFrame with the required format for 
	a bar plot

	Parameters:
	-----------
		n : int
			Number of points for each trace
		n_categories : int
			Number of categories for each point
		prefix : string
			Name for each category
		columns : [str]
			List of column names
		mode : string
			Format for each item
				'abc' for alphabet columns
				'stocks' for random stock names

def bars(n=3,n_categories=3,prefix='category',columns=None,mode='abc'):
	"""
	Returns a DataFrame with the required format for 
	a bar plot

	Parameters:
	-----------
		n : int
			Number of points for each trace
		n_categories : int
			Number of categories for each point
		prefix : string
			Name for each category
		columns : [str]
			List of column names
		mode : string
			Format for each item
				'abc' for alphabet columns
				'stocks' for random stock names
	"""		
	categories=[]
	if not columns:
		columns=getName(n,mode=mode)
	for i in range(n_categories):
		categories.extend([prefix+str(i+1)])
	data=dict([(x,np.random.randint(1,100,n_categories)) for x in columns])
	return pd.DataFrame(data,index=categories)