# Sorting by two values (basic sorting)
**URL:** https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961
**Category:** New to Julia
**Tags:** sort, arrays
**Created:** [March 11, 2021, 5:46pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961 "2021-03-11T17:46:43Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [March 11, 2021, 5:46pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/1 "2021-03-11T17:46:43Z")
This is probably fairly simple. I want to sort a set of tuples first by the second value, and then by the first value, like this:
```julia
julia> a = [rand(1:3,2) for i in 1: 5]
5-element Array{Array{Int64,1},1}:
[2, 1]
[3, 2]
[3, 2]
[1, 1]
[2, 1]
julia> sort!(a, by = x -> x[2])
5-element Array{Array{Int64,1},1}:
[2, 1]
[1, 1]
[2, 1]
[3, 2]
[3, 2]
julia> sort!(a, by = x -> x[1])
5-element Array{Array{Int64,1},1}:
[1, 1]
[2, 1]
[2, 1]
[3, 2]
[3, 2]
```
The result is perfectly fine. However, I am somewhat unsure if the result of the second sorting might be dependent on the sorting algorithm used. Am I safe with that?
In this case I really don’t care about performance, but I wonder if there is a special function or syntax for this kind of thing.
---
### Author:  [@Jeff\_Emanuel](https://discourse.julialang.org/u/Jeff_Emanuel)
#### Post date: [March 11, 2021, 5:53pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/2 "2021-03-11T17:53:22Z")
It is dependent on the algorithm, but the default Julia sort algorithm is stable, which means that equal keys will be in the same order after sort as before. You can supply a function to sort that gives the relative order of two elements. See the `lt` keyword argument.
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [March 11, 2021, 5:56pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/3 "2021-03-11T17:56:50Z")
> [@Jeff\_Emanuel](#):
>
> You can supply a function to sort that gives the relative order of two elements
Yes, of course, that is much smarter.
---
### Author:  [@jameson](https://discourse.julialang.org/u/jameson)
#### Post date: [March 11, 2021, 5:57pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/4 "2021-03-11T17:57:38Z")
> [@lmiq](#):
>
> ```julia
> julia> sort!(a, by = x -> x[1])
>
> ```
Those aren’t tuples, they’re vectors, and they already sort lexicographically. Thus, we can generically have `by` return the list of keys in order to compare:
```julia
julia> sort!(a, by=x -> (x[1], x[2]))
```
Which in this case is also just:
```julia
julia> sort!(a, by=identity)
```
or just
```julia
julia> sort!(a)
```
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [March 11, 2021, 6:00pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/5 "2021-03-11T18:00:45Z")
> [@jameson](#):
>
> Those aren’t tuples, they’re vectors
Yes, sorry, in the MWE I have used vectors, but my real case is with tuples. Good to know that, anyway.
---
### Author:  [@greg\_plowman](https://discourse.julialang.org/u/greg_plowman)
#### Post date: [March 11, 2021, 8:20pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/6 "2021-03-11T20:20:05Z")
> [@jameson](#):
>
> Thus, we can generically have `by` return the list of keys in order to compare:
>
> ```julia
> julia> sort!(a, by=x -> (x[1], x[2]))
>
> ```
>
> Which in this case is also just:
>
> ```julia
> julia> sort!(a, by=identity)
>
> ```
>
> or just
>
> ```julia
> julia> sort!(a)
>
> ```
Yes, but in this case, OP wants:
```julia
sort!(a, by = x -> (x[2], x[1]))
```
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [March 11, 2021, 8:56pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/7 "2021-03-11T20:56:29Z")
Actually there is a `isless` function defined for tuples that does what I want, it seems:
```julia
julia> a = [(rand(1:3),rand(1:3)) for i in 1: 5]
5-element Array{Tuple{Int64,Int64},1}:
(1, 3)
(1, 3)
(1, 2)
(3, 3)
(2, 1)
julia> sort!(a)
5-element Array{Tuple{Int64,Int64},1}:
(1, 2)
(1, 3)
(1, 3)
(2, 1)
(3, 3)
```
(I had to define a custom one because in my case the tuple was something computed from a struct, but that is another story).
---
### Author:  [@greg\_plowman](https://discourse.julialang.org/u/greg_plowman)
#### Post date: [March 11, 2021, 9:21pm UTC](https://discourse.julialang.org/t/sorting-by-two-values-basic-sorting/56961/8 "2021-03-11T21:21:59Z")
> [@lmiq](#):
>
> Actually there is a `isless` function defined for tuples that does what I want, it seems:
Yes, that’s what `sort!(a, by = x -> (x[2], x[1]))` uses