I need to loop through 1 table and read another until a value changes

Question

i need to read a table and sum the quantity field until a reason code changes.  how do I go about doing this?

Answer 1

sort itab by reasoncode.
Loop at itab.
quantiy = quanity  + itab-quantity.
at end of reasoncode.
jtab-reasoncode = itab-reasoncodee.
jtab-sum = quantity.
append jtab.
clear quantity.
endat
endloop.
or
sort itab  by reasoncode.
loop at itab.
at end of reasoncode.
sum.
jtab = itab.
append jtab.
endat.
endloop.
or
let us say itab and jtab are two tables and you want to loop through itab and read jtab for reasoncodes.
if jtab has only one entry for each entry in itab then use read else use loop.
loop at itab.
loop at jtab where reasoncode = itab-reasoncode.
quantiy = quantiy + jtab-quanity.
endloop.
endloop.
or
loop at itab.
read table jtab with key reasoncode = itab-reasoncode.
if sy-subrc eq 0.
endif
endloop.