I need to merge two pandas data frames using a columns which contains numerical values.   

For example, the two data frames could be like the following ones:   

**data frame "a"**

```
    a1   b1
0  "x"  13560
1  "y"  193309
2  "z"  38090
3  "k"  37212

```

**data frame "b"**

```
    a2    b2
0  "x"  13,56
1  "y"  193309
2  "z"  38,09
3  "k"  37212

```

What i need to do, is merge a with b on column b1/b2.   

The problem is that as you can see, some values of data frame b', are a little bit different. First of all, b' values are not integers but strings and furthermore, the values which end with 0 are "rounded" (13560 --> 13,56).

What i've tried to do, is replace the comma and then cast them to int, but it doesn't work; more in details this procedure doesn't add the missing zero.  

This is the code that i've tried:

```
b['b2'] = b['b2'].str.replace(",", "")
b['b2'] = b['b2'].astype(np.int64) # np is numpy

```

Is there any procedure that i can use to fix this problem?