I'm doing something wrong with merge and I can't understand what it is. I've done the following to estimate a histogram of a series of integer values:

import pandas as pnd
import numpy  as np

series = pnd.Series(np.random.poisson(5, size = 100))
tmp  = {"series" : series, "count" : np.ones(len(series))}
hist = pnd.DataFrame(tmp).groupby("series").sum()
freq = (hist / hist.sum()).rename(columns = {"count" : "freq"})

If I print hist and freq this is what I get:

> print hist
        count
series       
0           2
1           4
2          13
3          15
4          12
5          16
6          18
7           7
8           8
9           3
10          1
11          1

> print freq 
        freq
series      
0       0.02
1       0.04
2       0.13
3       0.15
4       0.12
5       0.16
6       0.18
7       0.07
8       0.08
9       0.03
10      0.01
11      0.01

They're both indexed by "series" but if I try to merge:

> df   = pnd.merge(freq, hist, on = "series")

I get a KeyError: 'no item named series' exception. If I omit on = "series" I get a IndexError: list index out of range exception.

I don't get what I'm doing wrong. May be "series" is an index and not a column so I must do it differently?

python pandas
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