Question: When updating one DataFrame based on info from second one the NaN's are not transferred.
With below code

```
import pandas as pd
import numpy as np
df1 = pd.DataFrame({'A':[1,2,3,4,5], 'B':[4,5,6,7,8]})
df2 = pd.DataFrame({'A':[1,2,3], 'B':[7,np.nan,6]})
df1.update(df2)

```

The new DataFrame will look as below:

[![enter image description here](https://i.stack.imgur.com/2JbAm.png)](https://i.stack.imgur.com/2JbAm.png)

So the value from df2 is not transferred as this is a NaN

[![enter image description here](https://i.stack.imgur.com/MPJy5.png)](https://i.stack.imgur.com/MPJy5.png)

Normally this is probably an expected outcome but not in the particular case that I'm working on.
For the moment how I deal with it is that I replace all NaNs with a value or string that signalizes to me that it's something I need to check but I was wondering if there is an actual solution to pass the NaN as an update?

[![enter image description here](https://i.stack.imgur.com/bWc7H.png)](https://i.stack.imgur.com/bWc7H.png)

Answer: 
Need a ternary operator which can control your data is ready or not if not CircularProgressIndicator() will shown at appbar unless you can see your data.For example you can be try to fetch data from db that can be take time or maybe you cant fetch data so in this stuation must be show a progress indicator when data ready progress indicator bar will execute.

```
String? foo;
Future fetchDummy()async{
foo = await dummyData
}

foo !=nul? Text("$foo") : CircularProgressIndicator()

```
You can create a variable of type duration and then create a function which returns a future builder which is going to await for the duration to finish then display the country but in the mean time will display a circular indicator