# Saving outputs in CSV file
**URL:** https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493
**Category:** General Usage
**Tags:** csv
**Created:** [August 7, 2020, 11:30am UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493 "2020-08-07T11:30:58Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 7, 2020, 11:30am UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/1 "2020-08-07T11:30:58Z")
This is my first time to use CSV to save outputs and i’m working on a small example to get used to it but it look like i’m still having troubles in it, here is the working example:
```julia
using CSV
using DataFrames
function mar(x,y)
open("myfile.csv", "a")
for i in 1:10
global s=x*i+y
end
end
```
then when i input this:
```julia
x=2
y=4
mar(x,y)
CSV.write("myfile.csv",x=x,y=y,s=s)
```
(generic function with 1 method)
but when i try to read the file it shows me that the file is empty
```julia
CSV.read("myfile.csv")
```
0 rows × 0 columns
i don’t know what is the thing that i’m doing wrong in here.
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [August 7, 2020, 1:11pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/2 "2020-08-07T13:11:03Z")
I answered your question previously on StackOverflow [here](https://stackoverflow.com/questions/63234061/how-to-save-the-outputs-of-a-code-in-csv-files-in-julia/63234578?noredirect=1#comment111900304_63234578).
Your main issue here is that you missed out a pair of parentheses when copying my answer:
```julia
CSV.write("out.csv", (s = s, x = x, y = y))
```
is what I put on SO, while you have
```julia
CSV.write("out.csv", s = s, x = x, y = y)
```
Note that in my answer, there are parentheses around `s=s, x=x, y=y` - this will construct a `NamedTuple`, which satisfies enough of the `Tables.jl` interface to be written out to csv by `CSV.write`.
There is an additional issue here compared to your SO post, which is that your `x` and `y` are scalars, while your `s` will be a vector. To construct the table you therefore need to decide what you want to put in the `x` and `y` columns. E.g. to repeat the `x` and `y` values in all rows you would do:
```julia
(s = s, x = fill(x, 10), y = fill(y, 10))
```
There are also a few unrelated issues in your code as well, which make me think that it’d be worthwhile for you to spend a day or two reading through the excellent Julia manual to get the hang of the language basics:
- You `open` the csv file in your `mar` function, but this actually isn’t necessary if you want to use `CSV.write` in the way I suggested;
- You have a `global` annotation in your loop, which in the context of your posted snippet doesn’t make sense, as `s` is not defined anywhere outside your function.
- You are `using DataFrames`, although this isn’t actually necessary in your case - `CSV.write` can handle a simple `NamedTuple` for writing out data, which you can construct without relying on any external dependencies.
- Your function doesn’t return anything - this might be related to the point above, as you might be attempting to structur your program as defining `s` outside the function and then use `mar` to mutate the global variable `s`. This is not a great way of going about things for many reasons, not least because non-constant globals are terrible for performance in Julia. Try writing your function such that they only depend on their arguments and return whatever value you want to calculate rather than mutate a global state.
Example:
```julia
using CSV
mar(x, y) = x .* collect(1:10) .+ y
x = 2; y = 4
s = mar(x, y)
```
---
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 8, 2020, 9:46am UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/3 "2020-08-08T09:46:59Z")
this example in general is just a working example before using `CSV` in my actual code and I just want to know how can I use `CSV` in case where we have a function because it’s not clear for me yet, maybe my example code wasn4t that clear enough, but the main point is for me to learn how can I use it if I have a function.
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [August 8, 2020, 9:49am UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/4 "2020-08-08T09:49:52Z")
Sorry but I still don’t understand your problem - what is keeping you from just using `CSV.write("out.csv", x)` where x is whatever NamedTuple/other table you want to write out to file in a function?
---
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 8, 2020, 9:57am UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/5 "2020-08-08T09:57:11Z")
I put
```julia
CSV.write("out.csv", s = s, x =fill(x, 10), y = fill(y, 10))
```
just right after the end of the loop and I close the function after I try to read the file
'CSV.read(“out.csv”)` and I get this
```julia
ArgumentError: "out.csv" is not a valid file
```
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [August 8, 2020, 10:25am UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/6 "2020-08-08T10:25:30Z")
Have another look at what I wrote in my original reply - you need parentheses around `s=s, x=fill(x,10), y=fill(y,10)`.
```julia
s = s, x = fill(x, 10), y = fill(y, 10)
```
is not the same as
```julia
(s = s, x = fill(x, 10), y = fill(y, 10))
```
See for yourself:
```julia
julia> x = 2; y = 4;
julia> s = x .* (1:10) .+ y;
julia> s = s, x = fill(x, 10), y = fill(y, 10)
ERROR: syntax: "10" is not a valid function argument name
Stacktrace:
[1] top-level scope at REPL[19]:1
julia> (s = s, x = fill(x, 10), y = fill(y, 10))
(s = 6:2:24, x = [2, 2, 2, 2, 2, 2, 2, 2, 2, 2], y = [4, 4, 4, 4, 4, 4, 4, 4, 4, 4])
```
So the reason `CSV.read` errors is that you never actually write a csv file with what you’re doing, because you’re not constructing a `NamedTuple` when you leave out the brackets.
Again I think it would be helpful to go through the Julia documentation to learn a bit more about the basics of the language.
---
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 8, 2020, 5:17pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/7 "2020-08-08T17:17:41Z")
even if I put the parentheses I still get the same error, like I said I know how to use it if we don4t have a function but in this case where I have a function I really don’t get it:
you can see here :
```julia
julia> using CSV
julia> function mar(x,y)
for i in 1:10
s=x*i+y
end
CSV.write("out.csv",(s = s, x =fill(x, 10), y = fill(y, 10)))
end
mar (generic function with 1 method)
julia> CSV.read("out.csv")
┌ Warning: `CSV.read(input; kw...)` is deprecated in favor of `CSV.read(input, DataFrame; kw...)
└ @ CSV C:\Users\Administrator\.julia\packages\CSV\vohbW\src\CSV.jl:41
ERROR: ArgumentError: "out.csv" is not a valid file
Stacktrace:
[1] CSV.Header(::String, ::Int64, ::Bool, ::Int64, ::Nothing, ::Int64, ::Bool, ::Nothing, ::Nothing, ::Bool, ::Nothing, ::Nothing, ::Array{String,1}, ::String, ::Nothing, ::Bool, ::Char, ::Nothing, ::Nothing, ::Char, ::Nothing, ::Nothing, ::UInt8, ::Array{String,1}, ::Array{String,1}, ::Nothing, ::Nothing, ::Dict{Type,Type}, ::Nothing, ::Float64, ::Bool, ::Bool, ::Bool, ::Bool, ::Bool, ::Bool) at C:\Users\Administrator\.julia\packages\CSV\vohbW\src\header.jl:92
[2] #File#26(::Int64, ::Bool, ::Int64, ::Nothing, ::Int64, ::Bool, ::Nothing, ::Nothing, ::Bool, ::Nothing, ::Nothing, ::Array{String,1}, ::String, ::Nothing, ::Bool, ::Char, ::Nothing, ::Nothing, ::Char, ::Nothing, ::Nothing, ::UInt8, ::Array{String,1}, ::Array{String,1}, ::Nothing, ::Nothing, ::Dict{Type,Type}, ::Nothing, ::Float64, ::Bool, ::Bool, ::Bool, ::Bool, ::Bool, ::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::Type{CSV.File}, ::String) at C:\Users\Administrator\.julia\packages\CSV\vohbW\src\file.jl:216
[3] CSV.File(::String) at C:\Users\Administrator\.julia\packages\CSV\vohbW\src\file.jl:216
[4] #read#75(::Bool, ::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}, ::typeof(CSV.read), ::String, ::Nothing) at C:\Users\Administrator\.julia\packages\CSV\vohbW\src\CSV.jl:44
[5] read at C:\Users\Administrator\.julia\packages\CSV\vohbW\src\CSV.jl:40 [inlined] (repeats 2 times)
[6] top-level scope at REPL[45]:1
```
I don’t know what i’m still missing
---
### Author:  [@lungben](https://discourse.julialang.org/u/lungben)
#### Post date: [August 8, 2020, 6:51pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/8 "2020-08-08T18:51:28Z")
In the code above, you are not executing the function mar, only defining it.
---
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 8, 2020, 7:59pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/9 "2020-08-08T19:59:40Z")
that’s my bad i forgot to put it, but if i execute it and then tried to read the file it’ll give me :
`0 rows × 0 columns` which means that nothing has been written in the file.
---
### Author:  [@lungben](https://discourse.julialang.org/u/lungben)
#### Post date: [August 8, 2020, 8:08pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/10 "2020-08-08T20:08:50Z")
I have no PC at hand to check, but from the code I guess that s is a scalar, whereas the other elements in the NamedTuple are vectors.
Could this cause the issue?
---
### Author:  [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)
#### Post date: [August 8, 2020, 9:55pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/11 "2020-08-08T21:55:40Z")
`s` is not defined at the point where you call `write`. It is also a scalar, which doesn’t work with `CSV.write`. The following works fine. Hopefully you can adapt it to what you need.
```julia
function mar(x,y)
for i in 1:10
s=x*i+y
end
CSV.write("out.csv",(s = [s], x = [x], y = [x]))
end
```
---
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 9, 2020, 12:14pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/12 "2020-08-09T12:14:29Z")
Yeah that works fine except it only shows me the last output when `i=10`, even if i put `CSV.write`befor the end of the loop it still shows me the last output only
```julia
julia> function mar(x,y)
for i in 1:10
s=x*i+y
end
CSV.write("out.csv",(s = [s], x = [x], y = [y]))
end
mar (generic function with 1 method)
julia> mar(10,2)
"out.csv"
julia> CSV.read("out.csv")
1×3 DataFrame
│ Row │ s │ x │ y │
│ │ Int64 │ Int64 │ Int64 │
├─────┼───────┼───────┼───────┤
│ 1 │ 110 │ 10 │ 2 │
```
---
### Author:  [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)
#### Post date: [August 9, 2020, 12:28pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/13 "2020-08-09T12:28:50Z")
What would you like to do? Save all x, y, and ś values? Right now you’re throwing all the intermediate values away. s at the end is just the last one.
---
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 9, 2020, 12:34pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/14 "2020-08-09T12:34:51Z")
yes i want to save all the x,y and s i know the `s` is the only one that will change with each iteration.
---
### Author:  [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)
#### Post date: [August 9, 2020, 12:48pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/15 "2020-08-09T12:48:17Z")
On mobile, so I can’t give you example code on this one. First, keep track of each value of s. Right now you do s = … each time, which throws away the last value of s. Then, copy x and y as many times as s is long. You can use fill for that, like in a previous example above.
@nilshg’s solution should work for you. Why doesnt it?
---
### Author:  [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)
#### Post date: [August 9, 2020, 1:05pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/16 "2020-08-09T13:05:45Z")
You need the keyword argument `append = true` in `CSV.write`. The default is `false`, which overwrites the file each time.
---
### Author:  [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)
#### Post date: [August 9, 2020, 1:44pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/17 "2020-08-09T13:44:16Z")
I’m not sure, but it sounds like @marouane isn’t concerned with writing multiple times to the same file, but rather that the call to `write` is only giving them a single row, when they expect it to be 10 rows because of the for-loop.
---
### Author:  [@pdeffebach](https://discourse.julialang.org/u/pdeffebach)
#### Post date: [August 9, 2020, 1:56pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/18 "2020-08-09T13:56:10Z")
Well, unless `CSV.write` is happening inside the loop, they shouldn’t expect multiple rows.
@marouane put the `CSV.write` call _inside_ the loop with `append = true`.
Realistically, note that a `Vector` of `NamedTuple`s can be saved to a file using CSV.jl. So you can also collect all the named tuples from your `for` loop into a vector and save that with a single `CSV.write` call.
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [August 9, 2020, 3:30pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/19 "2020-08-09T15:30:37Z")
Is this an MWE and you want to do something more complicated in reality? If not there’s no reason to call `CSV.write` multiple time with `append` in the loop, rather just collect all the stuff you want to write out in vectors and put them together into a `NamedTuple` like suggested originally.
E.g.
```julia
function mar(x,y)
s = zeros(10)
for i in 1:10
s[i] = x*i + y
end
CSV.write("out.csv",(s = s, x = fill(x, 10), y = fill(y, 10)))
end
```
---
### Author:  [@marouane](https://discourse.julialang.org/u/marouane)
#### Post date: [August 10, 2020, 1:12pm UTC](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493/20 "2020-08-10T13:12:44Z")
but still even using the `append=true` how come i’m still missing the first value where `i=1`
```julia
using CSV
function mar(x,y)
for i in 1:10
s=x*i+y
CSV.write("save.csv",(s = [s], x=[x], y=[y]),append=true)
end
end
x=2
y=4
mar(x,y)
CSV.read("save.csv")
```
9 rows × 3 columns
| | 6 | 2 | 4 |
| --- | --- | --- | --- |
| | Int64 | Int64 | Int64 |
| 1 | 8 | 2 | 4 |
| 2 | 10 | 2 | 4 |
| 3 | 12 | 2 | 4 |
| 4 | 14 | 2 | 4 |
| 5 | 16 | 2 | 4 |
| 6 | 18 | 2 | 4 |
| 7 | 20 | 2 | 4 |
| 8 | 22 | 2 | 4 |
| 9 | 24 | 2 | 4 |
[Next page](https://discourse.julialang.org/t/saving-outputs-in-csv-file/44493.md?page=2)