Using Python Pandas to bin data in one df according to bins defined in a second df

Question

I am attempting to bin data in one dataframe according to bins defined in a second dataframe. I am thinking that some combination of pd.bin and pd.merge might get me there?

This is basically the form each dataframe is currently in:

df = pd.DataFrame({'id':['a', 'b', 'c', 'd','e'],
                   'bin':[1, 2, 3, 3, 2],
                   'perc':[0.1,0.9,0.3,0.7,0.5]})

df2 = pd.DataFrame({'bin':[1, 1, 1, 2, 2, 2, 3, 3, 3], 
                    'result':['low', 'medium','high','low', 'medium','high','low', 'medium','high'],
                    'cut_min':[0,0.2,0.6,0,0.3,0.7,0,0.4,0.8],
                    'cut_max':[0.2,0.6,1,0.3,0.7,1,0.4,0.8,1]})

df:

bin id  perc
1   a   0.1
2   b   0.9
3   c   0.3
3   d   0.7
2   e   0.5

And this is the table with the bins, df2:

bin cut_max cut_min result
1   0.2     0.0     low
1   0.6     0.2     medium
1   1.0     0.6     high
2   0.3     0.0     low
2   0.7     0.3     medium
2   1.0     0.7     high
3   0.4     0.0     low
3   0.8     0.4     medium
3   1.0     0.8     high

I would like to match the bin, and find the appropriate result in df2 using the cut_min and cut_max that encompasses the perc value in df. So, I would like the resulting table to look like this:

bin id  perc    result
1   a   0.1     low
2   b   0.9     high
3   c   0.3     low
3   d   0.7     medium
2   e   0.5     medium

I originally wrote this in a SQL query which accomplished the task quite simply with a join:

select
  df.id
  , df.bin
  , df.perc
  , df2.result
from df
inner join df2
  on df.bin = df2.bin
  and df.perc >= df2.cut_min 
  and df.perc < df2.cut_max

If anyone knows a good way to do this using Pandas, it would be greatly appreciated! (And this is actually the first time I haven't been able to find a solution just searching on stackoverflow, so my apologies if any of the above wasn't explained well enough!)

Answer 1

First merge df and df2 on the bin column, and then select the rows where cut_min <= perc < cut_max:

In [95]: result = pd.merge(df, df2, on='bin').query('cut_min <= perc < cut_max'); result
Out[95]: 
    bin id  perc  cut_max  cut_min  result
0     1  a   0.1      0.2      0.0     low
5     2  b   0.9      1.0      0.7    high
7     2  e   0.5      0.7      0.3  medium
9     3  c   0.3      0.4      0.0     low
13    3  d   0.7      0.8      0.4  medium

In [97]: result = result[['bin', 'id', 'perc', 'result']]

In [98]: result.sort('id')
Out[98]: 
    bin id  perc  result
0     1  a   0.1     low
5     2  b   0.9    high
9     3  c   0.3     low
13    3  d   0.7  medium
7     2  e   0.5  medium