what is the dc component in the output of diode half wave rectifier circuit will it be the average value or the rms value of the output waveform?
The output waveform \$v_0\$ of a half wave rectifier consists of the positive pulses of the input signal, less a bit for the diode drop.

The DC component of that is defined as its average. That's the DC value that would appear after a while on the output of a lowpass filter connected to \$v_0\$.

The RMS value of \$v_0\$ is defined as the DC value that gives the equivalent heating in the load resistor.

The difference is small but significant for modestly rippling waveforms like this. There is no difference if \$v_0\$ is DC. The difference increases as the waveform becomes more spiky.

One way to see what's happening, which I understand not everybody will grok, is that the RMS value of the waveform measures the total power that's available in all its components, AC and DC. The average value measures the power of only the DC component. The difference between the DC value and the RMS value will therefore be a measure of the power available in the non-DC components, that is the AC power of the waveform. This means that we can say that \$ RMS \ge averageDC\$, always.

If you were to connect a capacitor across the output resistor, it would hold the peak voltage of \$v_0\$, which is larger than the RMS value of the input voltage \$v_I\$, a fact that often confuses the uninitiated.