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package org.rosuda.JRI;

// 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}).

<p>

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 2720 2007-03-15 17:35:42Z urbanek $

*/

public class RList extends Object {

/** xpressions containing head, body and tag.

The terminology is a bit misleading (for historical reasons) - head corresponds to CAR, body to CDR and finally tag is TAG. */

public REXP head, body, tag;

/** cached keys (from TAG) */

String[] keys = null;

/** cached values(from CAR) */

REXP[] values = null;

/** flag denoting whether we need to re-fetch the cached values.<p><b.Note:</b> the current assumption is that the contents don't change after first retrieval - there is currently no recursive check! */

boolean dirtyCache = true;

/** constructs an empty list */

public RList() { head=body=tag=null; }

/** fake constructor to keep compatibility with Rserve (for now, will be gone soon) */

public RList(RVector v) {

Vector n = v.getNames();

if (n != null) {

keys = new String[n.size()];

n.copyInto(keys);

}

values=new REXP[v.size()];

v.copyInto(values);

dirtyCache=false;

// head,tail,tag are all invalid!

}

/** constructs an initialized list

@param h head xpression

@param b body xpression */

public RList(REXP h, REXP b) { head=h; body=b; tag=null; }

/** constructs an initialized list

@param h head xpression (CAR)

@param t tag xpression (TAG)

@param b body/tail xpression (CDR)

*/

public RList(REXP h, REXP t, REXP b) { head=h; body=b; tag=t; }

/** get head xpression (CAR)

@return head xpression */

public REXP getHead() { return head; }

/** get body xpression (CDR)

@return body xpression */

public REXP getBody() { return body; }

/** get tag xpression

@return tag xpression */

public REXP getTag() { return tag; }

/** internal function that updates cached vectors

@return <code>true</code> if the conversion was successful */

boolean updateVec() {

if (!dirtyCache) return true;

// we do NOT run it recursively, because in most cases only once instance is asked

RList cur = this;

int l = 0;

while (cur!=null) {

l++;

REXP bd = cur.getBody();

cur = (bd==null)?null:bd.asList();

}

keys=new String[l];

values=new REXP[l];

cur = this;

l=0;

while (cur != null) {

REXP x = cur.getTag();

if (x!=null) keys[l]=x.asSymbolName();

values[l] = cur.getHead();

REXP bd = cur.getBody();

cur = (bd==null)?null:bd.asList();

l++;

}

dirtyCache=false;

return true;

}

/** 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 */

public REXP at(String v) {

if (!updateVec() || keys==null || values==null) return null;

int i=0;

while (i<keys.length) {

if (keys[i].compareTo(v)==0) return values[i];

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 */

public REXP at(int i) {

return (!updateVec() || values==null || i<0 || i>=values.length)?null:values[i];

}

/** returns all keys of the list

@return array containing all keys or <code>null</code> if list is not standartized */

public String[] keys() {

return (!updateVec())?null:this.keys;

}

}