I am trying to convert a column of Object dtype to float64

Pandas version - 2.21

I tried using convert\_objects() to force rows that cannot convert to NaN and was successful at converting my column to a float64

I want to know what rows/data did not allow me to convert it into a float64.
Is there a function out their that can do that ?

For example :

```
col1

2015
2016
NaN
NaN
3005
i_am_a_string
4006
another_string
5008
4005

df['col1'].astype(float64) 

FAILED!! because the column has string data and cannot convert them all to float64

```

My desired output I want to see those strings

```
i_am_a_string
another_string

```