Read File with HL7 messages and coun number of FT1

Assuming the stream contains the normal $C(13) segment delimiters:

Class User.HL7.Stream Extends %RegisteredObject
{

ClassMethod GetCounts(pStream As %Stream.FileCharacter, Output pMsgCount As %Numeric, Output pSegCounts As %ArrayOfDataTypes) As %Status
{
    Do pStream.Rewind()
    Set pStream.LineTerminator = $C(13)
    Set pSegCounts = 0
    While 'pStream.AtEnd
    {
        Set tLine = pStream.ReadLine()
        // Remove leading control characters
        Set tSeg = $ZSTRIP(tLine,"<C")
        // Get the segment name
        Set tSegName = $EXTRACT(tSeg,1,3)
        If tSegName '= ""
        {
            If '$DATA(pSegCounts(tSegName))
            {
                // We have a new subscript
                Set pSegCounts = pSegCounts + 1
                Set pSegCounts(tSegName) = 1
            }
            Else
            {
                Set pSegCounts(tSegName) = pSegCounts(tSegName) + 1
            }
        }
    }
    Set pMsgCount = pSegCounts("MSH")
    Return $$$OK
}

}

Call the classmethod with the stream as follows:

Do ##class(User.HL7.Stream).GetCounts(stream,.Msgs,.Counts)

Counts will be subscripted by the segment names found in the message stream. In the above example, you'll find the occurrence count of FT1 segments in Counts("FT1") and the number of messages will be in Counts("MSH"). The value returned in Msgs is the same as Counts("MSH").