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MedSignals / Unified Signals

MedSignals is an internal class in MedRepository that defines signal types and manages .signals files—dictionaries mapping signal names to their properties. Each MedRepository instance has a sigs object for basic .signals operations. All signal definitions are found in MedSignals.h.

When initializing a repository, one of the first steps is to read the signals configuration file (specified in the repository config) and set up all signal definitions.

What is a signal?

A signal type is a class defined in MedSignals.h and acts as a placeholder for signals. Signals represent actual data stored in the repository, each with a specific type. For example:

  • BYEAR, GENDER, TRAIN: Store a single float value, typically using the SVal type, or as a generic signal with one integer value channel: "V(i)"
  • Hemoglobin, Creatinine: Store a date and a float value, using SDateVal or STimeVal, or as a generic signal with one integer time channel and one float value channel: "T(i),V(f)"
  • BP: Stores a date and two short values (diastolic and systolic blood pressure), using SDateShort2, or as a generic signal: "T(i),V(s,s)"

Each signal has several properties, defined in the SignalInfo class:

  • name: Signal name
  • type: Type code (from the SigType enum) or a generic type string. You can use get_signal_generic_spec() on UniversalSigVec to get its generic signal string representation.
  • sid: Unique integer signal ID from the signals config file, used for fast indexing and efficient access. Maximum SID is MAX_SID_NUM (currently 100,000).
  • bytes_len: Number of bytes needed to store one element.
  • n_time_channels: Number of time channels.
  • n_val_channels: Number of value channels.

Signals must currently have a fixed size.

Unified Signals - Part I

Most medical record signals can be described as having zero or more time channels and zero or more value channels. Examples:

  • BYEAR: 0 time channels, 1 float value channel
  • Creatinine: 1 integer time channel, 1 float value channel
  • BP: 1 integer time channel, 2 float value channels
  • DM_Registry: 2 integer time channels, 1 int/char value channel

When time channels are integers and value channels are floats, signals can be accessed in a unified way, regardless of their type. This allows for generalized code in components like RepProcessors and FeatureGenerators in MedProcessTools.

See Part II for usage examples.

Current Signal Types

All signal types are defined in MedSignals.h. Available types include:

Signal Type Time Channels Value Channels Placeholders Example Signals
SVal 0 1 float BYEAR, TRAIN, GENDER
SDateVal 1 1 int : float Hemoglobin, Creatinine
STimeVal 1 1 long long : float Creatinine (mimic)
SDateRangeVal 2 1 int, int : float DM_Registry
STimeRangeVal 2 1 long long, long long : float (mimic)
STimeStamp 0 1 : long long (mimic)
SDateVal2 1 2 int : float, unsigned short Drugs (MHS)
STimeLongVal 1 1 long long : long long (mimic)
SDateShort2 1 2 int : short, short BP
SValShort2 0 2 : short, short (mimic)
SValShort4 0 4 : short, short, short, short (mimic)

Adding a New Signal Type

To add a new legacy signal type:

  1. Add an enum value for the type (used for encoding in the signals file).
  2. Define the signal class and its methods.
  3. Update MedConvert to read the new signal type (add parsing logic if needed).
  4. Make sure the new signal class inherits from UnifiedSig for unified signal compatibility.
  5. Implement these methods: - n_time_channels() - n_val_channels() - time_unit() - int Time(int chan) - float Val(int chan) - SetVal(chan, _val) - Set(int *times, float *vals) - Comparison operators (<, ==) - Output operator (<<)

Unified Signals - Part II

To work with unified signals, use the UniversalSigVec (usv) class. Instead of the standard get() method, use uget() to load signal data into a usv object. Key features:

  • Initialize for a specific signal type using only the enum.
  • Use uget() to load data (no copies; uses pointers and virtual functions).
  • Access any time or value channel uniformly across all signal types.

This lets you write type-independent code. Initialization has a performance cost, but repeated use with the same type is efficient.

Example Usage

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// Initialize repository and UniversalSigVec
MedRepository rep;
UniversalSigVec usv;

// ... initialize repository ...

rep.uget(pid, sid, usv);

// Print all time and value channels for each element
for (int i = 0; i < usv.len; i++) {
    for (int t_ch = 0; t_ch < usv.n_time_channels(); t_ch++)
        cout << "Element " << i << ", time channel " << t_ch << ": " << usv.Time(i, t_ch);
    for (int v_ch = 0; v_ch < usv.n_val_channels(); v_ch++)
        cout << "Element " << i << ", value channel " << v_ch << ": " << usv.Val(i, v_ch);
}

// Usage with PidRec
MedPidRepository pid_rep;
PidRec rec;

// ... initialize pid_rep ...

pid_rep.get_pid_rec(pid, rec);
rec.uget(sid, usv);

Signals Config File

For details on the signals file