Reading Files

Basic Event Loop

hipo::reader reader;
reader.open("data.hipo");

hipo::dictionary dict;
reader.readDictionary(dict);

hipo::bank particles(dict.getSchema("REC::Particle"));
hipo::event event;

while (reader.next()) {
    reader.read(event);
    event.read(particles);

    for (int row = 0; row < particles.getRows(); row++) {
        int   pid = particles.getInt("pid", row);
        float px  = particles.getFloat("px", row);
    }
}

Banklist Pattern (Preferred)

The banklist pattern is cleaner when reading multiple banks:

hipo::reader reader;
reader.open("data.hipo");

auto list = reader.getBanks({"REC::Particle", "REC::Event", "REC::Calorimeter"});

while (reader.next(list)) {
    auto& particles = list[0];
    auto& recEvent  = list[1];
    auto& calos     = list[2];

    for (int row = 0; row < particles.getRows(); row++) {
        int pid = particles.getInt("pid", row);
    }
}

hipoeventfile (Simplest)

hipo::hipoeventfile file("data.hipo");
hipo::bank particles(file.dictionary().getSchema("REC::Particle"));

for (auto& event : file) {
    event.read(particles);
    // process...
}

Random Access

Jump to a specific event by number:

reader.gotoEvent(5000);
reader.read(event);
event.read(particles);

Or jump to a specific record:

reader.gotoRecord(10);
// then iterate from there
while (reader.next()) { ... }

Tag Filtering

Only read events with specific tags:

reader.setTags({1, 2});  // set before iterating

while (reader.next()) {
    reader.read(event);
    // only events with tag 1 or 2 are returned
}

Column Index Caching

For performance-critical loops, cache column indices:

hipo::bank particles(dict.getSchema("REC::Particle"));
int pidCol = particles.getSchema().getEntryOrder("pid");
int pxCol  = particles.getSchema().getEntryOrder("px");
int pyCol  = particles.getSchema().getEntryOrder("py");
int pzCol  = particles.getSchema().getEntryOrder("pz");

while (reader.next(list)) {
    for (int row = 0; row < particles.getRows(); row++) {
        int   pid = particles.getInt(pidCol, row);
        float px  = particles.getFloat(pxCol, row);
        float py  = particles.getFloat(pyCol, row);
        float pz  = particles.getFloat(pzCol, row);
    }
}

Reading User Configuration

hipo::reader reader;
reader.open("data.hipo");

std::string runNumber = reader.readUserConfig("run");
printf("Run: %s\n", runNumber.c_str());

Listing Available Banks

hipo::dictionary dict;
reader.readDictionary(dict);

for (auto& name : dict.getSchemaList()) {
    printf("Bank: %s\n", name.c_str());
    dict.getSchema(name.c_str()).show();
}

Handling Missing Banks

A bank with 0 rows means it wasn't present in the event:

event.read(particles);
if (particles.getRows() == 0) {
    // REC::Particle not in this event
    continue;
}

Check if a schema exists before creating a bank:

if (dict.hasSchema("REC::Particle")) {
    hipo::bank particles(dict.getSchema("REC::Particle"));
}