# How to change the type of a column of a DataFrame
**URL:** https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074
**Category:** General Usage
**Tags:** question
**Created:** [October 19, 2019, 10:35am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074 "2019-10-19T10:35:45Z")
**Posts on this page:** 10
**Page:** 1
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [October 19, 2019, 10:35am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/1 "2019-10-19T10:35:45Z")
I have a DataFrame that has a few columns of the types “Union{Missing, String}” and “Union{Missing, Float64}”. But there are no missing values in the data.
I would like to change the type of these columns to either “String” or “Float64”. How can I achieve that?
---
### Author:  [@xiaodai](https://discourse.julialang.org/u/xiaodai)
#### Post date: [October 19, 2019, 11:02am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/2 "2019-10-19T11:02:53Z")
`disallowmissing` e.g.
```julia
using Missings
a = DataFrame(a = Union{Missing, String}["a", "b"])
a[!, :a] = disallowmissing(a[!, :a])
```
The reverse of `disallowmissing` is (you guessed it!) `allowmissing`
---
### Author:  [@ufechner7](https://discourse.julialang.org/u/ufechner7)
#### Post date: [October 19, 2019, 12:32pm UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/3 "2019-10-19T12:32:15Z")
Thank you for your explanation!
I couldn’t find this info in the manual: [Missing Values · The Julia Language](https://docs.julialang.org/en/v1/manual/missing/)
---
### Author:  [@xiaodai](https://discourse.julialang.org/u/xiaodai)
#### Post date: [October 19, 2019, 12:44pm UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/4 "2019-10-19T12:44:09Z")
There was a long story. Anyway, these fucntions are in [https://github.com/JuliaData/Missings.jl](https://github.com/JuliaData/Missings.jl)
Perhaps they should be part of base, but it’s in an external package
---
### Author:  [@Rojesh](https://discourse.julialang.org/u/Rojesh)
#### Post date: [January 1, 2021, 6:22am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/5 "2021-01-01T06:22:10Z")
In this same dataframe that allows missing
`a = DataFrame(a = Union{Missing, String}["a", "b"])`
if I try `push!(a,[nothing])`
I get an error: Cannot `convert` an object of type Nothing to an object of type String
It is a missing data, should missing allow nothing as well?
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [January 1, 2021, 6:58am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/6 "2021-01-01T06:58:50Z")
> [@Rojesh](#):
>
> It is a missing data, should missing allow nothing as well?
Typically `nothing` should not be used to represent missing data in the statistical sense.
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### Author:  [@Rojesh](https://discourse.julialang.org/u/Rojesh)
#### Post date: [January 1, 2021, 7:23am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/7 "2021-01-01T07:23:13Z")
Thanks @Tamas_Papp
I’m trying to push data from a JSON I got through a request which consist of nothing, I have to convert nothing in the JSON to missing before I can push it in the dataframe.
I converted the dataframe to accept any and push it and then replaced nothing with missing.
I was wondering if there was a better way.
---
### Author:  [@bkamins](https://discourse.julialang.org/u/bkamins)
#### Post date: [January 1, 2021, 7:53am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/8 "2021-01-01T07:53:17Z")
You can also do:
```julia
julia> a = DataFrame(a = Union{Missing, String}["a", "b"])
2×1 DataFrame
Row │ a
│ String?
─────┼─────────
1 │ a
2 │ b
julia> disallowmissing!(a, :a)
2×1 DataFrame
Row │ a
│ String
─────┼────────
1 │ a
2 │ bhich consist of nothing, I have to convert nothing in the JSON to missing before I can push it in the dataframe.
```
which is a bit more flexible as it allows you to pass any column selector and has `error` keyword argument.hich consist of nothing, I have to convert nothing in the JSON to missing before I can push it in the dataframe.
If you are `push!`-ing data to the data frame use `promote=true` to perform auto-promotion of column `eltype`s (although it would be better to do the conversion before pushing as @Tamas_Papp suggested).
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### Author:  [@StatisticalMouse](https://discourse.julialang.org/u/StatisticalMouse)
#### Post date: [January 1, 2021, 8:54am UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/9 "2021-01-01T08:54:51Z")
I had the same problem recently. I tried to use `transform!`, but I couldn’t make it work. I ended up using `dropmissing!`.
Do you have comments regarding using these two other functions for this task?
---
### Author:  [@bkamins](https://discourse.julialang.org/u/bkamins)
#### Post date: [January 1, 2021, 1:26pm UTC](https://discourse.julialang.org/t/how-to-change-the-type-of-a-column-of-a-dataframe/30074/10 "2021-01-01T13:26:16Z")
`transform!` would do it, e.g.:
```julia
transform!(df, :a => disallowmissing => :a)
```
but `dropmissing!` has `error` kwarg and it was introduced in DataFrames.jl before `transform!` was implemented.