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package org.rosuda.JRclient;

// JRclient library - client interface to Rserve, see http://www.rosuda.org/Rserve/
// Copyright (C) 2004 Simon Urbanek
// --- for licensing information see LICENSE file in the original JRclient distribution ---

import java.util.*;

/** implementation of R-lists<br>
    This is rather preliminary and may change in future since it's not really proper.
    The point is that the parser tries to interpret lists to be of the form entry=value,
    where entry is stored in the "head" part, and value is stored in the "body" part.
    Then using {@link #at(String)} it is possible to fetch "body" for a specific "head".
    The terminology used is partly from hash fields - "keys" are the elements in "head"
    and values are in "body" (see {@link #keys}).
    On the other hand, R uses lists to store complex internal structures, which are not
    parsed according to the structure - in that case "head" and "body" have to be evaluated
    separately according to their meaning in that context.

    @version $Id: RList.java 1330 2005-01-24 18:25:42Z urbaneks $
00023 public class RList extends Object {
    /** xpressions containing head and body. 
      The terminology is a bit misleading - head corresponds to CAR, body to CDR and finally tag is TAG. */
00026     public REXP head, body, tag;
    /** usual assumption is that both head and body are xpressions containing vectors.
      In such case the actual content objects (Vectors) are cached for key/value access. */
00029     Vector h,b;

    /** constructs an empty list */
00032     public RList() { head=body=tag=null; }
    /** constructs an initialized list
      @param h head xpression
      @param b body xpression */
00037     public RList(REXP h, REXP b) { head=h; body=b; tag=null; }
    /** get head xpression (CAR)
      @return head xpression */
00041     public REXP getHead() { return head; }
    /** get body xpression (CDR)
      @return body xpression */
00045     public REXP getBody() { return body; }

    /** get tag xpression
      @return tag xpression */
00049     public REXP getTag() { return tag; }

    /** internal function that updates cached vectors
        @return <code>true</code> if both expressions are vectors and of the same length */
00053     boolean updateVec() {
      if (head==null||body==null||
          return false;
      return (h.size()==b.size());

    /** get xpression given a key
      @param v key
      @return xpression which corresponds to the given key or
              <code>null</code> if list is not standartized or key not found */
00066     public REXP at(String v) {
      if (!updateVec()) return null;
      for (int i=0;i<h.size();i++) {
          REXP r=(REXP)h.elementAt(i);
          if (r!=null && r.Xt==REXP.XT_STR && ((String)r.cont).compareTo(v)==0)
            return (REXP)b.elementAt(i);
      return null;

    /** get element at the specified position
      @param i index
      @return xpression at the index or <code>null</code> if list is not standartized or
              if index out of bounds */
00080     public REXP at(int i) {
      if (!updateVec()) return null;
      return (i>=0 && i<b.size())?(REXP)b.elementAt(i):null;

    /** returns all keys of the list
      @return array containing all keys or <code>null</code> if list is not standartized */
00087     public String[] keys() {
      if (!updateVec()) return null;
      String[] k=new String[h.size()];
      for(int i=0;i<h.size();i++) {
          REXP r=(REXP)h.elementAt(i);
      return k;

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