{
"cells": [
{
"cell_type": "markdown",
"id": "a2630978",
"metadata": {},
"source": [
"# hist013_TH1_rebin\n",
"\n",
"This tutorial illustrates how to:\n",
" - create a variable bin-width histogram with a binning such\n",
" that the population per bin is about the same.\n",
" - rebin a variable bin-width histogram into another one.\n",
"\n",
"\n",
"\n",
"\n",
"**Author:** Rene Brun \n",
"This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Tuesday, May 19, 2026 at 08:12 PM."
]
},
{
"cell_type": "markdown",
"id": "f996588f",
"metadata": {},
"source": [
"create a fix bin histogram"
]
},
{
"cell_type": "code",
"execution_count": 1,
"id": "8793ad59",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:12:11.248719Z",
"iopub.status.busy": "2026-05-19T20:12:11.248573Z",
"iopub.status.idle": "2026-05-19T20:12:11.725787Z",
"shell.execute_reply": "2026-05-19T20:12:11.725150Z"
}
},
"outputs": [],
"source": [
"TH1F *h = new TH1F(\"h\", \"test rebin\", 100, -3, 3);\n",
"Int_t nentries = 1000;\n",
"h->FillRandom(\"gaus\", nentries);\n",
"Double_t xbins[1001];\n",
"Int_t k = 0;\n",
"TAxis *axis = h->GetXaxis();\n",
"for (Int_t i = 1; i <= 100; i++) {\n",
" Int_t y = (Int_t)h->GetBinContent(i);\n",
" if (y <= 0)\n",
" continue;\n",
" Double_t dx = axis->GetBinWidth(i) / y;\n",
" Double_t xmin = axis->GetBinLowEdge(i);\n",
" for (Int_t j = 0; j < y; j++) {\n",
" xbins[k] = xmin + j * dx;\n",
" k++;\n",
" }\n",
"}\n",
"xbins[k] = axis->GetXmax();"
]
},
{
"cell_type": "markdown",
"id": "2fac8d96",
"metadata": {},
"source": [
"create a variable bin-width histogram out of fix bin histogram\n",
"new rebinned histogram should have about 10 entries per bin"
]
},
{
"cell_type": "code",
"execution_count": 2,
"id": "f3a0191c",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:12:11.739241Z",
"iopub.status.busy": "2026-05-19T20:12:11.739104Z",
"iopub.status.idle": "2026-05-19T20:12:11.943251Z",
"shell.execute_reply": "2026-05-19T20:12:11.942646Z"
}
},
"outputs": [],
"source": [
"TH1F *hnew = new TH1F(\"hnew\", \"rebinned\", k, xbins);\n",
"hnew->FillRandom(\"gaus\", 10 * nentries);"
]
},
{
"cell_type": "markdown",
"id": "adc97b03",
"metadata": {},
"source": [
"rebin hnew keeping only 50% of the bins"
]
},
{
"cell_type": "code",
"execution_count": 3,
"id": "f980c3f2",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:12:11.945491Z",
"iopub.status.busy": "2026-05-19T20:12:11.945356Z",
"iopub.status.idle": "2026-05-19T20:12:12.149678Z",
"shell.execute_reply": "2026-05-19T20:12:12.148863Z"
}
},
"outputs": [],
"source": [
"Double_t xbins2[501];\n",
"Int_t kk = 0;\n",
"for (Int_t j = 0; j < k; j += 2) {\n",
" xbins2[kk] = xbins[j];\n",
" kk++;\n",
"}\n",
"xbins2[kk] = xbins[k];\n",
"TH1F *hnew2 = (TH1F *)hnew->Rebin(kk, \"hnew2\", xbins2);"
]
},
{
"cell_type": "markdown",
"id": "1213c3e8",
"metadata": {},
"source": [
"draw the 3 histograms"
]
},
{
"cell_type": "code",
"execution_count": 4,
"id": "41816de3",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:12:12.151562Z",
"iopub.status.busy": "2026-05-19T20:12:12.151431Z",
"iopub.status.idle": "2026-05-19T20:12:12.355783Z",
"shell.execute_reply": "2026-05-19T20:12:12.355004Z"
}
},
"outputs": [],
"source": [
"TCanvas *c1 = new TCanvas(\"c1\", \"c1\", 800, 1000);\n",
"c1->Divide(1, 3);\n",
"c1->cd(1);\n",
"h->Draw();\n",
"c1->cd(2);\n",
"hnew->Draw();\n",
"c1->cd(3);\n",
"hnew2->Draw();"
]
},
{
"cell_type": "markdown",
"id": "e848a9eb",
"metadata": {},
"source": [
"Draw all canvases "
]
},
{
"cell_type": "code",
"execution_count": 5,
"id": "cc632e32",
"metadata": {
"collapsed": false,
"execution": {
"iopub.execute_input": "2026-05-19T20:12:12.357986Z",
"iopub.status.busy": "2026-05-19T20:12:12.357864Z",
"iopub.status.idle": "2026-05-19T20:12:12.577538Z",
"shell.execute_reply": "2026-05-19T20:12:12.576933Z"
}
},
"outputs": [
{
"data": {
"text/html": [
"\n",
"\n",
"\n",
"
\n",
"\n",
"\n",
"\n"
],
"text/plain": [
""
]
},
"metadata": {},
"output_type": "display_data"
}
],
"source": [
"%jsroot on\n",
"gROOT->GetListOfCanvases()->Draw()"
]
}
],
"metadata": {
"kernelspec": {
"display_name": "ROOT C++",
"language": "c++",
"name": "root"
},
"language_info": {
"codemirror_mode": "text/x-c++src",
"file_extension": ".C",
"mimetype": " text/x-c++src",
"name": "c++"
}
},
"nbformat": 4,
"nbformat_minor": 5
}