@Override ValFrame apply(Env env, Env.StackHelp stk, AST asts[]) { Frame fr = stk.track(asts[1].exec(env)).getFrame(); double frac = asts[2].exec(env).getNum(); double nrow = fr.numRows() * frac; Vec vecs[] = fr.vecs(); long[] idxs = new long[fr.numCols()]; int j = 0; for (int i = 0; i < idxs.length; i++) if (vecs[i].naCnt() < nrow) idxs[j++] = i; Vec vec = Vec.makeVec(Arrays.copyOf(idxs, j), null, Vec.VectorGroup.VG_LEN1.addVec()); return new ValFrame(new Frame(vec)); }