[julia-users] Re: What is the best way to get two by two tables in Julia?

[Dan]

Hi Arin,
It would be helpful to have more details about the input (a dataframe?) and 
output (a two-by-two table or a table indexed by categories?). Some code to 
give context to the question would be even more help (possibly in another 
language, such as R).

Having said this, here is a starting point for some code:

If these packages are missing Pkg.add works:

using NamedArrays
using DataFrames
using RDatasets

Gets the dataset and makes some categorical variables in DataFrames style:

iris = dataset("datasets","iris")
iris[:PetalWidth] = PooledDataArray(iris[:PetalWidth])
iris[:Species] = PooledDataArray(iris[:Species])

Define function for a `twobytwo` and a general categorical table 
`crosstable`:

function twobytwo(data::DataFrame,cond1,cond2)
       nres= NamedArray(zeros(Int,2,2),Any[[false,true],[false,true]],[
"cond1","cond2"])
       for i=1:nrow(data)
           nres[Int(cond1(data[i,:]))+1,Int(cond2(data[i,:]))+1] += 1
       end
       nres
end

function crosstable(data::DataFrame,col1,col2)
       @assert isa(data[col1],PooledDataArray)
       @assert isa(data[col2],PooledDataArray)
       nres= NamedArray(zeros(Int,length(data[col1].pool),length(data[col2].
pool)),Any[data[col1].pool,data[col2].pool],[col1,col2])
       for i=1:nrow(data)
           nres[data[col1].refs[i],data[col2].refs[i]] += 1
       end
       nres
end

Finally, using the functions, make some tables:

tbt = twobytwo(iris,r->r[1,:Species]=="setosa",r->r[1,:PetalWidth]>=1.5)
ct = crosstable(iris,:PetalWidth,:Species)

My summary and conclusions:
1) Julia is general purpose and with a little familiarity any data handling 
is possible.
2) This is a basic data exploration operation and there must be some easy 
way to do this.

Waiting for more opinions/solutions on this question, as it is also basic 
for my needs.

Thanks for the question.

On Sunday, November 22, 2015 at 3:34:56 AM UTC+2, Arin Basu wrote:
>
> Hi All,
>
> Can you kindly advise how to get a simple way to do two by two tables in 
> Julia with two categorical variables. I have tried split-apply-combine (by 
> function) and it works with single variables, but with two or more 
> variables, I cannot get the table I want. 
>
> This is really an issue if we need to do statistical data analysis in 
> Epidemiology. 
>
> Any help or advice will be greatly appreciated.
>
> Arin Basu
>