import org.apache.spark.rdd$.$RDD

def matrixVectorMultiply$($M: RDD$[(($Int$,$ Int$),$ Double$)],$ v: RDD$[($Int$,$ Double$)])$: RDD$[($Int$,$ Double$)]=\{$

val MJoined $=$ M$.$map $\{$ case $(($i$,$ j$),$ value$)=>($j$,($i$,$ value$))\}$

val result $=$ MJoined.join$($v$)$

$.$map $\{$ case $(\_,(($i$,$ Mvalue$),$ vectorValue$))=>($i$,$ Mvalue $*$ vectorValue$)\}$

$.$reduceByKey$(\_+\_)$

result

$\}$

how to do matrix vecotor multiplication in one map reduce step?