Accessing labels of secondary tick marks

ROOT
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1

Hello everyone,

I am having trouble accessing the labels of secondary tick marks in a log axis. In practice, I would like to keep the primary tick mark labels, and some of the secondary ones. I provide an example below:

    TH1D *h = new TH1D("h", "some histogram", 5, 0, 2.1);
    for (int i=0; i<5; i++) {
        for (int j=0; j<=i; j++) h->Fill(i*0.42);
    }
    h->GetXaxis()->SetTitle("ln(0.4/x)");

    TCanvas *c = new TCanvas("c", "second axis", 800, 600);
    h->Draw();

    c->SetBottomMargin(0.3);

    auto axis = new TGaxis(2.1, 0.02, 0. ,0.02, 0.048982571, 0.4, 2,"NIGS-");
    axis->SetTitle("x");
    axis->CenterTitle();
    axis->SetTitleFont(43);
    axis->SetTitleSize(20);
    axis->SetTitleOffset(1.2);
    axis->SetLabelFont(43);
    axis->SetLabelSize(20);
    axis->SetLabelOffset(0.05);
    axis->SetTickSize(0.02);
    axis->SetMoreLogLabels(); // add the secondary tick labels
    // axis->ChangeLabel(1,-1,-1,-1,-1,-1,"-#pi");
    axis->ChangeLabel(510,-1,-1,-1,-1,-1,"this");
    axis->SetNoExponent();
    axis->Draw();

So the second axis is a log axis, where I want to keep from the secondary tick labels the 0.4, 0.3, 0.2 and 0.05, and get rid of the ones between 0.05 and 0.1, but with ChangeLabel() so far I have only managed to access the primary tick mark 0.1.

I am using ROOT 6.14 and can easily access up to 6.28.

Thanks in advance,
Lida

ROOT Version: 6.14
Platform: Centos 7

2

Hi Lida,

You can try to “erase” axis labels providing labSize argument 0:

    axis->ChangeLabel(1,-1,0);
    axis->ChangeLabel(2,-1,0);

Here 1 and 2 are labels indexes. See more info in documentation

In newer ROOT versions you also can modify axis labels by its values:

    axis->ChangeLabelByValue(0.05,-1,0);
    axis->ChangeLabelByValue(0.06,-1,0);

Regards,
Sergey

3

Dear Sergey,

Thanks for your response.

Unfortunately, ChangeLabel() has only worked for the primary tick marks in version 6.14. Meaning ChangeLabel(1,-1,0) affects the 0.1 label in the example above. I tried accessing the secondary labels with labNum=100 following the ndiv numbering scheme but it didn’t work.

I ended up installing version 6.30 on my own machine and I see that ChangeLabel(1, -1, 0) in this version actually affects the rightmost label (0.05) instead. Odd change from version to version.

I would really like to replicate this behavior in version 6.14 if possible, as it is the version on the machine at my institute.

Cheers,
Lida

4

Hi,

Version 6.14 is really old and most probably has bugs - which were fixed afterwards.

The only I can recommend - try experimentally which labNum value suppress labels.

Regards,
Sergey

5

Hi Sergey,

Thanks for your help. I will probably end up doing the cosmetic changes on a newer version.

Best,
Lida