Parallel Computing for Data Science

3.6. IMPROVED VERSION 55

# whose f i r s t index i s p s e t s t a r t

dochunk2 <− function ( p s e t s t a r t , x , y , xpx , xpy ,

allcombs , c hun k s i ze ) {

ncombs <− length ( allcombs )

l a s t t a s k <− min( p s e t s t a r t+c hunksiz e −1,ncombs )

t ( sapply ( allcombs [ p s e t s t a r t : l a s t t a s k ] , do1pset1 ,

x , y , xpx , xpy ) )

}

# f i n d th e a d j u s t e d R−s q u a red va l u e s f o r t h e g iv e n

# p r e d i c t o r s e t index

do1 pset1 <− function ( onepset , x , y , xpx , xpy ) {

ps <− c ( 1 , o n e p s e t +1) # a ccount f o r con s ta n t term

x1 <− x [ , ps ]

xpx1 <− xpx [ ps , ps ]

xpy1 <− xpy [ ps ]

ar2 <− l i n