Working with n rows in a df
#### Code Sample, a copy-pastable example if possible

```python
# Your code here

```
#### Problem description

[this should explain **why** the current behaviour is a problem and why the expected output is a better solution.]

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#### Expected Output

#### Output of ``pd.show_versions()``

<details>

So I have 3 different df. 2 of those df are per minute sensor readings and 3rd df is per hour readings.
I'm concatenating the 2 dfs in to a new df of per minute readings and I want to work on this new df (per minute values), do regression, get slope for every hour and then concatenate this new df2 with per hour slope readings with the 3rd df with per hour readings. Any idea how I do that? I hope I've explained the problem well. So basically I want to work with 60 rows. I'm new to pandas and this is my first issue on github. Please help and be gentle please. :) 
