# Using \`isnan()\` with missing values leads to hard to find bugs
**URL:** https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399
**Category:** General Usage
**Created:** [April 11, 2020, 3:31pm UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399 "2020-04-11T15:31:46Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@00krishna](https://discourse.julialang.org/u/00krishna)
#### Post date: [April 11, 2020, 3:31pm UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399/1 "2020-04-11T15:31:46Z")
I found some curious behavior when using the `isnan()`function on a dataframe with missing values the other day.
I was trying to replace NaN values with missing values in the dataframe. However, I found that when
I encountered `isnan(missing)` that this evaluated to `missing` instead of True or False. This was generating errors in the code that were hard to find, since the error message was related to the if-else function instead of the isnan() function.
I was just wondering if this was expected behavior. Seems a bit odd that a boolean function would return a non-boolean value like missing. But that could just be my simple mind’s way of thinking of things.
Anyhow, just wondering if this is really an issue I should submit, or if this is expected behavior? Thanks.
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### Author:  [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)
#### Post date: [April 11, 2020, 3:50pm UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399/2 "2020-04-11T15:50:50Z")
This is expected behavior. The value in question is `missing`, so we don’t know what the value is. It could be `NaN`, since we can’t know for sure, `isnan` returns missing.
Can i ask what language you are coming from? Different languages have different approaches to missing values.
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### Author:  [@00krishna](https://discourse.julialang.org/u/00krishna)
#### Post date: [April 11, 2020, 10:08pm UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399/3 "2020-04-11T22:08:14Z")
@pdeffebach Okay cool, good to know. I am coming from Python and R background. It just caught me by surprise that a boolean would return a missing value, instead of True or False. But that is okay, now I know to check for missing values before using the `isnan()` or other similar functions.
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### Author:  [@tbeason](https://discourse.julialang.org/u/tbeason)
#### Post date: [April 11, 2020, 10:24pm UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399/4 "2020-04-11T22:24:28Z")
You could do something like this
```julia
isnanmissing(x::Union{Number,Missing}) = ismissing(x) ? true : isnan(x)
```
which returns true if the number is missing or NaN
---
### Author:  [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)
#### Post date: [April 11, 2020, 10:30pm UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399/5 "2020-04-11T22:30:06Z")
Yes it’s a bit more strict than R.
In R you use `na.rm = T` everywhere. The equivalent usage would be to pass `skipmissing(x)` to all your functions. Another solution is to do `replace`
```julia
julia> replace(x, NaN => 0, missing => 100)
```
Check out [Missing.jl](https://github.com/JuliaData/Missings.jl) for convenience functions.
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### Author:  [@00krishna](https://discourse.julialang.org/u/00krishna)
#### Post date: [April 12, 2020, 1:34am UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399/6 "2020-04-12T01:34:15Z")
Oh yes, that makes a lot more sense. I forgot that `skipmissing()` existed, so I can use that. Sounds good, thanks for setting me straight.
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### Author:  [@00krishna](https://discourse.julialang.org/u/00krishna)
#### Post date: [April 12, 2020, 1:35am UTC](https://discourse.julialang.org/t/using-isnan-with-missing-values-leads-to-hard-to-find-bugs/37399/7 "2020-04-12T01:35:53Z")
Oh great, yes this will work. Nice, I will add this function to my little code library for future use. I am slowly starting to get a handle on the julia idioms. Thanks again.