BUG: Pandas Dataframe is converting float variable to integer
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**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
     
    df_mle.at[words_of_bigram[0], words_of_bigram[1]] = (df_bigram.at[i,'BigramCount']/frequencies.at['Frequency',words_of_bigram[0]])


```

#### Problem description

When I assigned the answer of the division which is a decimal value ( like 0.5) then value stored in the df_mle variable is an integer (like 0).

#### Expected Output
print(df_mle.at[words_of_bigram[0], words_of_bigram[1]])
>>> 0.5

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

<details>

[paste the output of ``pd.show_versions()`` here leaving a blank line after the details tag]

</details>
