# Indices in file names?
**URL:** https://discourse.julialang.org/t/indices-in-file-names/26376
**Category:** New to Julia
**Created:** [July 15, 2019, 8:05am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376 "2019-07-15T08:05:26Z")
**Posts on this page:** 17
**Page:** 1
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 15, 2019, 8:05am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/1 "2019-07-15T08:05:26Z")
Hi,
If I’m sending data to a CSV file in a for loop function, this means that I would need multiple files for each run, but how do I ensure that the file names would be different so that overwriting is avoided? I thought maybe an index in the file for each loop, but I don’t know how. For example,
```julia
for i = 1:n
.
.
.
CSV.write("Solution Table.csv", df)
end
```
So for each loop I want a separate solution file, but right now it just gets overwritten and only one file is generated. Any help would be appreciated, thanks!
---
### Author:  [@pmarg](https://discourse.julialang.org/u/pmarg)
#### Post date: [July 15, 2019, 8:13am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/2 "2019-07-15T08:13:03Z")
You can interpolate the index:
```julia
for i in 1:n
.
CSV.write("Solution Table$i.csv",df)
end
```
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 15, 2019, 8:21am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/3 "2019-07-15T08:21:23Z")
Sweet! Thank you sir
---
### Author:  [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)
#### Post date: [July 15, 2019, 8:22am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/4 "2019-07-15T08:22:35Z")
another approach
```julia
const filecount = Ref(0)
basename = "data"
extension = "csv"
function nextfilename(fileprefix=basename, ext=extension)
newcount = filecount[] + 1
filecount[] = newcount
newfilename = string(fileprefix, "_", newcount, ".", ext)
return newfilename
end
```
It runs like this
```julia
julia> nextfile = nextfilename()
"data_1.csv"
julia> nextfile = nextfilename()
"data_2.csv"
julia> nextfile = nextfilename()
"data_3.csv"
```
To include the full directory path, use
```julia
const filecount = Ref(0)
basename = "data"
extension = "csv"
dirpath = "/home/working/data"
function nextfilename(fileprefix=basename, ext=extension, dir=dirpath)
newcount = filecount[] + 1
filecount[] = newcount
newfilename = string(fileprefix, "_", newcount, ".", ext)
return joinpath(dir,newfilename)
end
julia> nextfile = nextfilename()
"/home/working/data/data_1.csv"
julia> nextfile = nextfilename()
"/home/working/data/data_2.csv"
julia> nextfile = nextfilename()
"/home/working/data/data_3.csv"
```
And, of course, you may initialize the `filecount` to wherever you may have left off when generating many files over several sessions.
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 15, 2019, 8:44am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/5 "2019-07-15T08:44:20Z")
That’s pretty interesting, thanks for the alternative.
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 17, 2019, 11:59am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/6 "2019-07-17T11:59:51Z")
Just a quick question, would it be possible to do this for variables and other names as well?
I know you can just use regular indices like `a[i] = x + i` etc, but for some names such as CSV or Dataframe variables, they don’t work?
For example
```julia
for i = 1:2
csv[i] = CSV.File(File_Df[i,1])
```
The above code doesn’t work however, or at least the way I did it doesn’t work. The $ symbol only works in strings, and I can’t use them for these names. Any advice would be appreciated
---
### Author:  [@pmarg](https://discourse.julialang.org/u/pmarg)
#### Post date: [July 17, 2019, 1:03pm UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/7 "2019-07-17T13:03:54Z")
I am not sure what you want to achieve with the filenames but you can access `DataFrames` columns via interpolation:
```julia
df = DataFrame(A1 = 1:4, A2 = 1:4)
for i in 1:2
println(df[!,Symbol("A$i")])
end
```
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 18, 2019, 5:13am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/8 "2019-07-18T05:13:19Z")
Oh okay, basically what I’m trying to do is name `DataFrames` with indices. So in a for loop, I want to name the `DataFrames` with the corresponding indices, for example `DataFrame1` when `i = 1` ,
`DataFrame2` when `i = 2` etc. So it’s the exact same initial question in this topic, but instead of naming an actual file, I’m trying to name a `DataFrame`. I tried the $ interpolation method but it didn’t work.
Hope that somewhat makes it clearer. Thanks!
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [July 18, 2019, 5:25am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/9 "2019-07-18T05:25:19Z")
> [@MuadhF](#):
>
> Oh okay, basically what I’m trying to do is name `DataFrames` with indices.
It cannot be done directly, as `DataFrame` only supports symbols for column names.
You can convert to `string`, then `Symbol`, eg
```julia
julia> DataFrame(Symbol("1") => 1:2, Symbol("2") => 3:4)
2×2 DataFrame
│ Row │ 1 │ 2 │
│ │ Int64 │ Int64 │
├─────┼───────┼───────┤
│ 1 │ 1 │ 3 │
│ 2 │ 2 │ 4 │
```
but I would advise against this, there is probably a less convoluted way.
Why do you need this?
Does the object need to be a `DataFrame`, or would a `Dict{Int,Vector}` or `Vector{Vector}` work better?
---
### Author:  [@pmarg](https://discourse.julialang.org/u/pmarg)
#### Post date: [July 18, 2019, 5:36am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/10 "2019-07-18T05:36:45Z")
There is an old (given Julia’s age) discussion here: [Redirecting to Google Groups](https://groups.google.com/forum/#!topic/julia-users/us7abUVhDHw)
You can read the pros and cons and some suggestions for alternative approaches. I agree with @Tamas_Papp that one should think why is this preferred compared to a `Dict` or even an `Array`. In any case, you can try something like this:
```julia
for n in 1:10
@eval $(Symbol("DataFrame_$n")) = $n
end
```
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 18, 2019, 6:13am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/11 "2019-07-18T06:13:18Z")
> [@Tamas\_Papp](#):
>
> Why do you need this?
>
> Does the object need to be a `DataFrame` , or would a `Dict{Int,Vector}` or `Vector{Vector}` work better?
I’m quite new to Julia, so right now I honestly am not sure what is better, but I’ll tell you what I’m trying to do, and forgive me if it’s not concise. I have a set of input CSV files that I want the Julia to read, a pair of files for each iteration. So I put the directories of these files into another CSV file (`Input files.csv`). I then created a DataFrame with a string column of all these input files (`File_Df`), and then in the for loop, using that DataFrame I created more dataframes for variable assignment later. I know this probably sounds confusing and inefficient, so I’ll provide part of the code and hopefully it’ll make sense, and I hope there is a better way to do it.
```julia
Input_Files = CSV.File("C:\\Users\\Muadh\\.atom\\Input files.csv", header = false)
File_Df = DataFrame(Input_Files)
for i = 1:length(Input_Files)
Df1 = DataFrame(CSV.File(File_Df[i,1]))
Df2= DataFrame(CSV.File(File_Df[i,2]))
kE = Df1[1,2]
d = Df1[2,2]
```
I’m guessing this is a very inefficient way, so please advise if there is a better way to do it. Regarding the file names, this is where I wanted to name the DataFrames in the for loop with indices so that I can have separate DataFrames without being overwritten.
Sorry for the long post once again, any advice would be greatly appreciated.
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [July 18, 2019, 6:20am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/12 "2019-07-18T06:20:36Z")
You example code was probably cut off while pasting. Do you need the `kE` and the `d` as pairs?
The key issue here is not really efficiency, but in what format you want your data eventually. This depends on what you want to _do_ with it.
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 18, 2019, 6:26am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/13 "2019-07-18T06:26:15Z")
Oh no they’re just variables that are being assigned values from the DataFrame. I didn’t paste everything as I thought it was not relevant, but here it is.
```julia
Input_Files = CSV.File("C:\\Users\\Muadh\\.atom\\Input files.csv", header = false)
File_Df = DataFrame(Input_Files)
for i = 1:length(Input_Files)
Df1 = DataFrame(CSV.File(File_Df[i,1]))
Df2= DataFrame(CSV.File(File_Df[i,2]))
kE = Df1[1,2]
d = Df1[2,2]
x = Df1[3,2]
T = round(Int, Df1[4,2])
CT = Df1[5,2]
D = Df1[6,2]
k_yearly = Df1[7,2]
```
So these are all variables that take values from the CSV files via the DataFrame. The objective of my code is an optimization model, so these are just variables that go into constraints.
---
### Author:  [@pmarg](https://discourse.julialang.org/u/pmarg)
#### Post date: [July 18, 2019, 7:20am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/14 "2019-07-18T07:20:30Z")
If `Input files.csv` contains the paths like this:
```julia
/..../path1.csv
/..../path2.csv
/..../path.csv
...
```
then you can try:
```julia
Input_Files = CSV.File("C:\\Users\\Muadh\\.atom\\Input files.csv", header = false) |> DataFrame
df = DataFrame.(CSV.File.(Input_Files[!,:Column1]))
```
you obtain a `n-element Array{DataFrame,1}:` of `DataFrames` and you can access it via
`df[1]`, `df[2]`, …`df[n]`. There is no need to create all these variable names dynamically.
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 18, 2019, 7:27am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/15 "2019-07-18T07:27:04Z")
I tried that, but I’m getting
```julia
ERROR: LoadError: MethodError: no method matching getindex(::DataFrame, ::typeof(!), ::Symbol)
Closest candidates are:
getindex(::DataFrame, ::Integer, ::Symbol) at C:\Users\Muadh\.julia\packages\DataFrames\0Em9Q\src\dataframe\dataframe.jl:327
getindex(::DataFrame, ::AbstractArray{T,1} where T, ::Union{Signed, Symbol, Unsigned}) at C:\Users\Muadh\.julia\packages\DataFrames\0Em9Q\src\dataframe\dataframe.jl:337
getindex(::DataFrame, ::Colon, ::Union{Signed, Symbol, Unsigned}) at C:\Users\Muadh\.julia\packages\DataFrames\0Em9Q\src\dataframe\dataframe.jl:358
...
Stacktrace:
[1] top-level scope at none:0
in expression starting at untitled-811a74ece6c83e1b6ec45450a45a95fe:5
```
---
### Author:  [@pmarg](https://discourse.julialang.org/u/pmarg)
#### Post date: [July 18, 2019, 7:29am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/16 "2019-07-18T07:29:25Z")
Try this one:
```julia
Input_Files = CSV.File("C:\\Users\\Muadh\\.atom\\Input files.csv", header = false) |> DataFrame
df = DataFrame.(CSV.File.(Input_Files[:Column1]))
```
Maybe you have an older version of `DataFrames`? Try to `up` because there is a slight change in the `DataFrames` syntax very recently.
---
### Author:  [@MuadhF](https://discourse.julialang.org/u/MuadhF)
#### Post date: [July 18, 2019, 7:51am UTC](https://discourse.julialang.org/t/indices-in-file-names/26376/17 "2019-07-18T07:51:32Z")
Thank you very much! I updated the pkg and it worked.