# Can't Convert 'Nothing' to 'Missing'

**URL:** <https://discourse.julialang.org/t/cant-convert-nothing-to-missing/42303>\
**Category:** General Usage\
**Tags:** question\
**Created:** [June 30, 2020, 1:51pm UTC](https://discourse.julialang.org/t/cant-convert-nothing-to-missing/42303 "2020-06-30T13:51:58Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![compleat](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/compleat/32/8958_2.png) [@compleat](https://discourse.julialang.org/u/compleat)\
**Post date:** [June 30, 2020, 1:51pm UTC](https://discourse.julialang.org/t/cant-convert-nothing-to-missing/42303/1 "2020-06-30T13:51:58Z")

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There has been a bit of discussion on here about ‘nothing’ vs ‘missing’ and why both are needed. I don’t really have an opinion on this as long as I can easily convert, which I can’t.

I tried the suggestion on Github [missing vs nothing #1854] which was marked as the solution:

replace( df.A , nothing =\> missing)

and it didn’t complain but didn’t work (‘nothings’ still there).

I wondered why the ! wasn’t needed and also why I didn’t need to broadcast, but attempting either of those led to an error.

Does anyone have any ideas?

Thanks

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**Author:** ![evanfields](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/evanfields/32/1744_2.png) [@evanfields](https://discourse.julialang.org/u/evanfields)\
**Post date:** [June 30, 2020, 2:00pm UTC](https://discourse.julialang.org/t/cant-convert-nothing-to-missing/42303/2 "2020-06-30T14:00:51Z")

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`replace` sans `!` returns a copy of the collection with the given replacement, but doesn’t modify in place. To modify in place, use `replace!`. So if you do e.g.

```julia
using DataFrames
df = DataFrame(x = [1, nothing, 3])
replace(df.x, nothing => missing)

```

Then the last line will just return `[1, missing, 3]` without modifying your DataFrame. Note that replacing `nothing` with `missing` will tend to require a new array type, and so `replace!` will throw an error. (E.g. an array with element type `Union{Int64, Nothing}` can’t hold values of type `Missing`.) Therefore, you’ll probably want to change dataframe columns by `df.A = replace(df.A, nothing => missing)`.

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**Author:** ![compleat](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/compleat/32/8958_2.png) [@compleat](https://discourse.julialang.org/u/compleat)\
**Post date:** [June 30, 2020, 2:17pm UTC](https://discourse.julialang.org/t/cant-convert-nothing-to-missing/42303/3 "2020-06-30T14:17:30Z")

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Hi Thanks, That is what I thought. But when I added the ! it threw an error:

julia\>replace(pt[:Age],nothing=\>missing);

julia\> replace!(pt[:Age],nothing=\>missing);  
Warning: `getindex(df::DataFrame, col_ind::ColumnIndex)` is deprecated, use `df[!, col_ind]` instead.  
caller = top-level scope at REPL[722]:1  
@ Core REPL[722]:1  
ERROR: MethodError: Cannot `convert` an object of type Missing to an object of type Int64

Thanks again  
PS I edited out the first Warning about using pt[:Age] which is not relevant.

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**Author:** ![Tamas\_Papp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tamas_papp/32/25949_2.png) [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)\
**Post date:** [June 30, 2020, 2:19pm UTC](https://discourse.julialang.org/t/cant-convert-nothing-to-missing/42303/4 "2020-06-30T14:19:57Z")

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The array element type cannot accommodate `missing`. You can use `replace`, replacing the entire column, eg

```julia
df.col = replace(df.col , nothing => missing)

```

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<div class="post-metadata">

**Author:** ![compleat](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/compleat/32/8958_2.png) [@compleat](https://discourse.julialang.org/u/compleat)\
**Post date:** [June 30, 2020, 2:20pm UTC](https://discourse.julialang.org/t/cant-convert-nothing-to-missing/42303/5 "2020-06-30T14:20:40Z")

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I see. Great. Thanks [worked]