Use custom iterator for speed
Use custom iterator for speed

jnishi/chainer,delta2323/chainer,wkentaro/chainer,ktnyt/chainer,hvy/chainer,ysekky/chainer,anaruse/chainer,keisuke-umezawa/chainer,rezoo/chainer,keisuke-umezawa/chainer,wkentaro/chainer,ktnyt/chainer,okuta/chainer,okuta/chainer,cupy/cupy,wkentaro/chainer,niboshi/chainer,keisuke-umezawa/chainer,hvy/chainer,okuta/chainer,cupy/cupy,pfnet/chainer,wkentaro/chainer,tkerola/chainer,aonotas/chainer,niboshi/chainer,jnishi/chainer,ktnyt/chainer,cupy/cupy,hvy/chainer,niboshi/chainer,hvy/chainer,jnishi/chainer,kashif/chainer,keisuke-umezawa/chainer,chainer/chainer,okuta/chainer,niboshi/chainer,chainer/chainer,chainer/chainer,cupy/cupy,chainer/chainer,ronekko/chainer,kiyukuta/chainer,jnishi/chainer,ktnyt/chainer