# How to leave only unique rows of array
**URL:** https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332
**Category:** General Usage
**Created:** [March 30, 2024, 4:46pm UTC](https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332 "2024-03-30T16:46:07Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@programista](https://discourse.julialang.org/u/programista)
#### Post date: [March 30, 2024, 4:46pm UTC](https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332/1 "2024-03-30T16:46:07Z")
These are two columns of a string matrix. How to leave only unique rows of these 12 array rows? :
```Kalinka
Kalinka surname
Kalinka surname
Kalinka surname
Kalinka geographical_name
Kalinka geographical_name
Kalinka geographical_name
Kalinka geographical_name
Kalinko surname
Kalinko surname
Kalinka name
Kalinka name
```
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [March 30, 2024, 5:53pm UTC](https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332/2 "2024-03-30T17:53:05Z")
See [Unique (indices) method similar to MATLAB](https://discourse.julialang.org/t/unique-indices-method-similar-to-matlab/34446) — for example, if you have a matrix `a` and you want the rows corresponding to whether columns 1 and 2 are unique, you could do:
```julia
julia> a = [ "Kalinka" "surname"
"Kalinka" "surname"
"Kalinka" "surname"
"Kalinka" "geographical_name"
"Kalinka" "geographical_name"
"Kalinka" "geographical_name"
"Kalinka" "geographical_name"
"Kalinko" "surname"
"Kalinko" "surname"
"Kalinka" "name"
"Kalinka" "name"];
julia> idx = unique(i -> (a[i,1], a[i,2]), axes(a, 1))
4-element Vector{Int64}:
1
4
8
10
julia> a[idx,:] # rows where (col1, col2) are unique
4×2 Matrix{String}:
"Kalinka" "surname"
"Kalinka" "geographical_name"
"Kalinko" "surname"
"Kalinka" "name"
```
```julia
```
---
### Author:  [@Dan](https://discourse.julialang.org/u/Dan)
#### Post date: [March 30, 2024, 6:24pm UTC](https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332/3 "2024-03-30T18:24:45Z")
Also, you can consider using DataFrames:
```julia
using DataFrames
using CSV
s = """name cname
Kalinka surname
Kalinka surname
Kalinka surname
Kalinka geographical_name
Kalinka geographical_name
Kalinka geographical_name
Kalinka geographical_name
Kalinko surname
Kalinko surname
Kalinka name
Kalinka name"""
f = IOBuffer(s)
df = CSV.read(f, DataFrame)
```
Now `unique` drops repeating lines:
```julia
julia> unique(df)
4×2 DataFrame
Row │ name cname
│ String7 String31
─────┼────────────────────────────
1 │ Kalinka surname
2 │ Kalinka geographical_name
3 │ Kalinko surname
4 │ Kalinka name
```
---
### Author:  [@programista](https://discourse.julialang.org/u/programista)
#### Post date: [March 30, 2024, 6:33pm UTC](https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332/4 "2024-03-30T18:33:09Z")
Big Thx, But apart from the columns I showed, I have others columns that I cannot lose. How to select entire unique rows of columns 2 and 3 from a 3-column matrix. Another way is how to get the numbers of unique rows mat[:,2:3]? julia\> mat
20×3 Matrix{Any}:
“aa” “aa” “”
“Aachen” “Aachen” “nazwa\_geograficzna”
“AAP” “AAP” “nazwa\_instytucji”
“Aarona” “Aaron” “imię”
“Aaron” “Aaron” “imię”
“Aaronach” “Aaron” “imię”
“Aaronami” “Aaron” “imię”
“Aaronem” “Aaron” “imię”
“Aaroni” “Aaron” “imię”
“Aaronie” “Aaron” “imię”
“Aaronom” “Aaron” “imię”
“Aaronowi” “Aaron” “imię”
“Aaronowie” “Aaron” “imię”
“Aaronów” “Aaron” “imię”
“Aarony” “Aaron” “imię”
“aaronowa” “aaronowy” “”
“aaronową” “aaronowy” “”
“aaronowe” “aaronowy” “”
“aaronowego” “aaronowy” “”
“aaronowej” “aaronowy” “”
---
### Author:  [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)
#### Post date: [March 30, 2024, 7:32pm UTC](https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332/5 "2024-03-30T19:32:58Z")
I really recommend you use DataFrames.jl for this task. Is there a reason you want to keep it a matrix?
---
### Author:  [@rocco\_sprmnt21](https://discourse.julialang.org/u/rocco_sprmnt21)
#### Post date: [March 30, 2024, 8:26pm UTC](https://discourse.julialang.org/t/how-to-leave-only-unique-rows-of-array/112332/6 "2024-03-30T20:26:26Z")
```julia
stack(unique(e->(e[2],e[3]),eachrow(m)),dims=1)
```
```julia
function runique(m, cols)
idx=Vector{Int}(undef,size(m, 1))
u=NaN
ui=1
for r in axes(m, 1)
if u!= @view m[r,cols]
idx[ui]=r
ui+=1
u= @view m[r,cols]
end
end
@views m[idx[1:ui-1],:]
end
```
```julia
using DataFrames
df=DataFrame(m,:auto)
combine(first,groupby(df,[:x2,:x3]))
```
but the best, as many suggest, is
```julia
unique(df,[:x2,:x3])
```