The correct method for the number 3 is the muonEnergyFraction():
    float chf = component(1).fraction();
    float nhf = component(5).fraction();
    float phf = component(4).fraction();
    float muf = component(3).fraction();
    float elf = component(2).fraction();

https://github.com/CERN-PH-CMG/cmg-cmssw/blob/a875832047532c5469aa9795751f0363cd5d9244/AnalysisDataFormats/CMGTools/src/PFJet.cc#L55