# DataFrame; create new column of integers representing strings in other column
**URL:** https://discourse.julialang.org/t/dataframe-create-new-column-of-integers-representing-strings-in-other-column/92268
**Category:** New to Julia
**Tags:** dataframes
**Created:** [December 29, 2022, 1:05pm UTC](https://discourse.julialang.org/t/dataframe-create-new-column-of-integers-representing-strings-in-other-column/92268 "2022-12-29T13:05:38Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@spk](https://discourse.julialang.org/u/spk)
#### Post date: [December 29, 2022, 1:05pm UTC](https://discourse.julialang.org/t/dataframe-create-new-column-of-integers-representing-strings-in-other-column/92268/1 "2022-12-29T13:05:38Z")
Hi all,
Just a real bone question regarding DataFrames and how to create a new column containing integers to represent each unique string in another column. Sorry if my example is a bit rubbish, I’m new to Julia and not the best coder to begin with… Anyway, I have a DataFrame with a String31 column containing 53 unique site names. I am attempting to create another column containing integers (1:53), with each integer representing each unique site, if that makes sense. As an example (I don’t know how to add code):
> test = DataFrame(site = [“site\_one”, “site\_two”, “site\_three”], charcoal = [0.789, 0.232, 0.451])
gives me:
> 3×2 DataFrame
> Row │ site charcoal
> │ String Float64
> ──┼──────────────────────
> 1 │ site\_one 0.789
> 2 │ site\_two 0.232
> 3 │ site\_three 0.451
So far, I have been trying:
> test[:, :site\_int] = map(test[:, :site]) do b
> if b == “site\_one”
> 1
> elseif b == “site\_two”
> 2
> elseif b == “site\_three”
> 3
> else
> missing
> end
> end
And it seems to work, but I can’t work out how to loop it/vectorise it to number each of the 53 sites; I am guessing there is a more sophisticated way of achieving this than just typing out each site name and assigning a value.
I hope this makes sense and someone could give me a hand in working it out. Any help greatly appreciated.
Cheers
Gregg
Sorry, I forgot to give an example of what I want:
> 3×3 DataFrame
> Row │ site charcoal site\_int
> │ String Float64 Int64
> ─────┼────────────────────────────────
> 1 │ site\_one 0.789 1
> 2 │ site\_two 0.232 2
> 3 │ site\_three 0.451 3
---
### Author:  [@bkamins](https://discourse.julialang.org/u/bkamins)
#### Post date: [December 29, 2022, 1:24pm UTC](https://discourse.julialang.org/t/dataframe-create-new-column-of-integers-representing-strings-in-other-column/92268/2 "2022-12-29T13:24:08Z")
The standard way to do it is to use CategoricalArrays.jl:
```julia
julia> using CategoricalArrays
julia> test.site_int = levelcode.(categorical(test.site))
3-element Vector{Int64}:
1
3
2
```
Note that:
1. by default levels are sorted in ascending order (but you can use any order you like - see the `levels!` function).
2. It is likely that you actually want `CategoricalVector` created with `categorical(test.site)` and not an integer code. What do you want to use these integer codes for?
If you just want integer indices (and do not need/like CategoricalArrays.jl funtionality) you can do:
```julia
julia> transform!(groupby(test, :site), groupindices => :site_int)
3×3 DataFrame
Row │ site charcoal site_int
│ String Float64 Int64
─────┼────────────────────────────────
1 │ site_one 0.789 1
2 │ site_two 0.232 2
3 │ site_three 0.451 3
```
or just
```julia
julia> uv = unique(test.site)
3-element Vector{String}:
"site_one"
"site_two"
"site_three"
julia> dict = Dict(uv .=> 1:length(uv))
Dict{String, Int64} with 3 entries:
"site_two" => 2
"site_one" => 1
"site_three" => 3
julia> [dict[x] for x in test.site]
3-element Vector{Int64}:
1
2
3
```
---
### Author:  [@spk](https://discourse.julialang.org/u/spk)
#### Post date: [December 29, 2022, 1:36pm UTC](https://discourse.julialang.org/t/dataframe-create-new-column-of-integers-representing-strings-in-other-column/92268/3 "2022-12-29T13:36:08Z")
Hi, that’s boss, cheers man, Yeah, the site names are not ordinal, I just want to represent them with a number. I am trying to recode some of my old hierarchical models from R in Julia/Turing. This model, in R, is a GLMM with site as a random effect, though when I try it using Turing it can’t check the index bounds of strings; I assumed it required an integer value, and it does work when I use such a format.
---
### Author:  [@spk](https://discourse.julialang.org/u/spk)
#### Post date: [December 29, 2022, 1:47pm UTC](https://discourse.julialang.org/t/dataframe-create-new-column-of-integers-representing-strings-in-other-column/92268/4 "2022-12-29T13:47:15Z")
Just to let you know,
> julia\> transform!(groupby(test, :site), groupindices =\> :site\_int)
didn’t work for me. It just returned the error code:
> ERROR: ArgumentError: Unrecognized column selector: DataFrames.groupindices =\> :site\_int
The bottom bit worked good though, cheers.
---
### Author:  [@bkamins](https://discourse.julialang.org/u/bkamins)
#### Post date: [December 29, 2022, 2:06pm UTC](https://discourse.julialang.org/t/dataframe-create-new-column-of-integers-representing-strings-in-other-column/92268/5 "2022-12-29T14:06:08Z")
@spk - please update your DataFrames.jl installation. You must be on some old version of the package. If you used DataFrames.jl 1.4 release it would work.