# How to create a NamedTuples from dynamic field names (for a df to dict converter)
**URL:** https://discourse.julialang.org/t/how-to-create-a-namedtuples-from-dynamic-field-names-for-a-df-to-dict-converter/5359
**Category:** General Usage
**Tags:** question, data
**Created:** [August 13, 2017, 3:51pm UTC](https://discourse.julialang.org/t/how-to-create-a-namedtuples-from-dynamic-field-names-for-a-df-to-dict-converter/5359 "2017-08-13T15:51:14Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)
#### Post date: [August 13, 2017, 3:51pm UTC](https://discourse.julialang.org/t/how-to-create-a-namedtuples-from-dynamic-field-names-for-a-df-to-dict-converter/5359/1 "2017-08-13T15:51:15Z")
I am trying to write a converter from DataFrame to Dict where the key is a NamedTuples, but I am stuck on how to create the NamedTuples when the “names” are not hard coded but stored in an array:
```julia
using NamedTuples
dimCols = [:colour,:shape,:border]
dimValues = ["blue","square","slim"]
#rowKey = @NT(colour,shape,border) # This works
rowKey = @NT(eval(dimCols...)) # This doesn't
a = rowKey(dimValues...)
```
I did consider as alternative to create the key one by one with `merge`, but I remained unsuccessful.
---
### Author:  [@bramtayl](https://discourse.julialang.org/u/bramtayl)
#### Post date: [August 13, 2017, 4:32pm UTC](https://discourse.julialang.org/t/how-to-create-a-namedtuples-from-dynamic-field-names-for-a-df-to-dict-converter/5359/2 "2017-08-13T16:32:58Z")
```julia
using NamedTuples
dimCols = [:colour,:shape,:border]
dimValues = ["blue","square","slim"]
equals(x, y) = Expr(:(=), x, y)
eval(:($NamedTuples.@NT $(equals.(dimCols, dimValues)...)))
```
Not sure why you would want to do this though… If you’re looking for type-stable access to dataframes you should probably be using DataFramesMeta, Query, or LazyQuery
---
### Author:  [@sylvaticus](https://discourse.julialang.org/u/sylvaticus)
#### Post date: [August 15, 2017, 9:39am UTC](https://discourse.julialang.org/t/how-to-create-a-namedtuples-from-dynamic-field-names-for-a-df-to-dict-converter/5359/3 "2017-08-15T09:39:57Z")
Thank you, my idea wasn’t related to type-stability but to have a handle way to write multidimensional equations, like:
[V[r,p,t] = V[r,p,t-1] + Growth[r,p,t] for r in regions, p in products, t in years[2:end] ]
I can do it using normal tuples as keys, but having named tuples I thought it would have allowed me to call the variables with the dimensions in whatever order irrespectively to the original one, e.g.
[V[time=t,reg=r,prod=p] = V[r,p,t-1] + Growth[r,p,t] for r in regions, p in products, t in years[2:end] ]
This however doesn’t work as:
```julia
using NamedTuples
myTupleDict = Dict(("aa","bb") => 1, ("aa","cc") =>2)
myNamedTupleDict = Dict(@NT(one = "aa", two = "bb") =>1, @NT(one = "aa", two = "cc") => 2)
myTupleDict[("aa","bb")] # 1
myNamedTupleDict[("aa","bb")] # KeyError
myNamedTupleDict[(two="bb",one="aa")] # KeyError
```
I hence misinterpreted NamedTuples, as I thought that the whole point would have been to get:
```julia
@NT(one = "aa", two = "bb") == @NT(two = "bb", one = "aa") == @NT("aa", "bb") == ("aa", "bb")
```
My implementation of the toDict() function is as follow, but it is pretty useless given the above point:
```julia
using DataFrames, NamedTuples
df = DataFrame(
colour = ["green","blue","white","green","green"],
shape = ["circle", "triangle", "square","square","circle"],
border = ["dotted", "line", "line", "line", "dotted"],
area = [1.1, 2.3, 3.1, 4.2, 5.2]
)
function toDict(df, dimCols, valueCol)
toReturn = Dict()
equals(x, y) = Expr(:(=), x, y)
for r in eachrow(df)
keyValues = []
for d in dimCols
push!(keyValues,r[d])
end
rowKey = eval(:($NamedTuples.@NT $(equals.(dimCols, keyValues)...)))
toReturn[rowKey] = r[valueCol]
end
return toReturn
end
myDict = toDict(df,[:colour,:shape,:border],:area)
```
Do you think there is an easy way to obtain the desired behaviour or should I forget NamedTuples for this approach ?
---
### Author:  [@bramtayl](https://discourse.julialang.org/u/bramtayl)
#### Post date: [August 15, 2017, 1:59pm UTC](https://discourse.julialang.org/t/how-to-create-a-namedtuples-from-dynamic-field-names-for-a-df-to-dict-converter/5359/4 "2017-08-15T13:59:19Z")
Something like this?
```julia
assignments = :(regions = 1), :(products = 2)
macro reorder(assignments...)
dict = Dict(map(assignments) do assignment
assignment.args
end)
:($CartesianIndex($(dict[:regions]), $(dict[:products]), $(dict[:years])))
end
@reorder products = 1 years = 2 regions = 5
```