How to combine separate month and year columns into one column in igor?

// Make some waves representing year and month
Make/O/N=(3*4) year = 2000 + trunc(p/4)
Make/O/N=(3*4) month = mod(3*p+1,12)
Edit year, month

// Make a wave to hold date/time data
Make/O/N=(3*4)/D dt         // Wave must be double-precision
dt = date2secs(year, month, 1)  // Create date/time values from the year and month
SetScale d, 0, 0, "dat", dt     // Tell Igor it is a date/time wave
AppendToTable dt

// Make a graph using the dt wave for the X axis
Make/O/N=(3*4) someData = p
Display someData vs dt

// Set the date format of the X axis. I generated this command using the
// Date Format popup menu in the Ticks&Grids tab of the Modify Axis dialog.
ModifyGraph dateInfo(bottom)={0,0,-1},dateFormat(bottom)={Default,2,2,1,2,"Month/Year",16}

// Set the bottom axis label
Label bottom "\\u#2Date"        // \\u suppresses Igor's default units mechanism