Hello,
I was wondering whether ROOT has the option for plotting chord diagrams, see: Help Online - Origin Help - Chord Diagram/Chord Diagram with Ratio Layout
circularGraph - File Exchange - MATLAB Central
If not, maybe it can be implemented in the future as a class derived from TGraphPolar using TPolyLines?
Thanks for the attention.
ROOT does not have such diagram. It would required a new implementation. It is circular but I am not sure it should derive from TGraphPolar.
I do not think that TGraphPolar is good starting point - it always drawing polar coordinates.
Chord diagram and circular graph is absolutely new kind of draw options, which could be implemented for the TH2 class. I could try to implement this in JSROOT.
What would be the format of data ? what kind of ROOT data do you want to show ?
As said here:
A chord diagram represents flows or connections between several entities (called nodes ).
I am not sure which kind of ROOT data will map this.
May be a TH2 with the same alpha numeric labels along X and Y ? each label would be “a node” and the content of each bin gives the strength of the connection between two nodes and therefore the thickness of the line connecting them ?
So that will be a special case of TH2
In MATLAB, the data is expressed as a 2D matrix.
The strength of connection between nodes i and j are just matrix[i][j]. The diagonal matrix[i][i] is zero. The matrix should be symmetric matrix[i][j] = matrix[j][i]. (Or it should be specified if it’s the lower or the upper triangular matrix that will be considered for plotting)
I agree, a TH2 could work well, but it would be good if it would also support passing a raw C array (2D matrix).
Also, it would be great if the transparency and color of the connecting line, not just the thickness, can be set as function of strength.
Here is a “quick and dirty” macro producing a circular graph. It is really just the basic structure … nothing you can use … just the idea:
TCanvas *c1;
void chord(TH2F *h)
{
c1->cd(2)->Range(-1, -1, 1, 1);;
TEllipse *circle = new TEllipse(0., 0., 0.8);
circle->SetLineWidth(1);
circle->Draw("L");
TAxis *xaxis;
xaxis=h->GetXaxis();
THashList *labels = xaxis->GetLabels();
int ndiv = xaxis->GetLast()-xaxis->GetFirst()+1;
float da = 2*TMath::Pi()/ndiv;
float ax = 0 ;
float ay = 0;
for (int i=1; i<=ndiv; i++) {
for (int j=1; j<=ndiv; j++) {
if (h->GetBinContent(i,j)>0){
auto l = new TLine(0.8*TMath::Cos(ax), 0.8*TMath::Sin(ax),
0.8*TMath::Cos(ay), 0.8*TMath::Sin(ay));
l->SetLineWidth(h->GetBinContent(i,j));
l->SetLineColor(h->GetBinContent(i,j));
l->Draw();
}
ay = ay+da;
}
ay = 0;
ax = ax+da;
}
TIter next(labels);
auto t= new TText();
t->SetTextAlign(22);
t->SetTextSize(0.03);
auto m = new TMarker();
m->SetMarkerStyle(20);
float a = 0;
while (TObject *obj = next()) {
t->DrawText(0.85*TMath::Cos(a), 0.85*TMath::Sin(a), obj->GetName());
m->DrawMarker(0.8*TMath::Cos(a), 0.8*TMath::Sin(a));
a = a+da;
}
}
void chord_diagrams()
{
const Int_t n = 12;
const char *L[n] = {"A","B","C","D","E","F","G","H","I","J","K","L"};
c1 = new TCanvas("c","c",10,10,1200,600);
c1->Divide(2,1);
auto *h = new TH2F("h","",n,0,1,n,0,1);
h->SetStats(0);
for (int i=0;i<n;i++) h->Fill(L[i],L[i],0);
h->Fill(L[2],L[3],1);
h->Fill(L[3],L[2],1);
h->Fill(L[5],L[3],2);
h->Fill(L[3],L[5],2);
h->Fill(L[9],L[4],5);
h->Fill(L[4],L[9],5);
c1->cd(1)->SetGrid();
h->Draw("text");
chord(h);
}
Cool, thanks
I guess that the second for loop should stop at j<i ? (To not draw twice the same, as it’s symmetrical?)
As I said it is just a quick and dirty prototype. Fell free to improve it. The initialization and filling of the histogram can be improved too as the histogram used has some strict characteristics.
Hi,
I slightly modify Olivier macro:
void chord_diagrams()
{
const Int_t n = 12;
const char *L[n] = {"A","B","C","D","E","F","G","H","I","J","K","L"};
c1 = new TCanvas("c","c",10,10,1200,600);
c1->Divide(2,1);
auto *h = new TH2F("h","",n,0,1,n,0,1);
h->SetStats(0);
for (int i=0;i<n;i++) h->Fill(L[i],L[i],0);
h->Fill(L[2],L[3],1);
h->Fill(L[3],L[2],1);
h->Fill(L[5],L[3],2);
h->Fill(L[3],L[5],2);
h->Fill(L[9],L[4],5);
h->Fill(L[4],L[9],5);
c1->cd(1)->SetGrid();
h->Draw("text");
c1->cd(2);
h->Draw("circular");
}
This is produced canvas:
To get it working, with current root master do:
[shell] export JSROOTSYS=https://jsroot.gsi.de/dev/
[shell] root --web chord_diagrams.C
Later I will commit modified JSROOT code into ROOT repository.
After that ROOT will work directly - without need to set JSROOTSYS variable.
I also want to implement chord diagram - it should be also relatively simple.
Regards,
Sergey
Looks nice ! The next step might be to make some special methods to book and fill “chord histograms” as they are really special:
Hi @ferhue,
I now implement “chord” drawing option, taking already provided functionality
of d3.js - see Chord Diagram / D3 / Observable
If in the macro “chord” instead of “circle” option is specified, output will be:
Regards,
Sergey
So beautiful!
Thanks so much for the prompt implementation!!
