Additional field in SAP Infoset - internal table

Hi Gurus,

I have invoices like:

VBELN Matnr mtart

1234 Ek21 MCFE

1234 Ek33 MCFE

1234 Ek29 MCFE

1234 321 MRM1

_______________________

1235 EK11 MCFE

1235 EK17 MCFE

_______________________

3212 EK23 MCFE

3212 EK33 MCFE

How can create additional field in SAP infoset, what show in every line in invoice, that invoice have line with mtart = u2018MRM1u2019 or mtart <> u2018MRM1u2019. Aim is to filter invoices with line mtart = MRM1

VBELN Matnr mtart result

1234 Ek21 MCFE 1

1234 Ek33 MCFE 1

1234 Ek29 MCFE 1

1234 321 MRM1 1

_______________________

1235 EK11 MCFE 0

1235 EK17 MCFE 0

_______________________

3212 EK23 MCFE 0

3212 EK33 MCFE 0

How can create additional field in SAP Infoset?