[R] Program advice

[John Logsdon]

Hi

Starting to use R as a serious tool, I have come across a programming
problem that I can't see the answer too yet.  Can someone advise me plese.

The problem is that I want to plot a series of lines which represent short
term growths.  All the data is in a single vector and I can indicate
the index via a second vector.  In GLIM, if the second vector is a factor,
a single $GRA Size Year Item instruction will do it with a factor

Example data:
Item    Size  Year
1       0     1980
1       10    1981
1       14    1982
1       20    1983
1       25    1984
1       30    1985
2       0     1980
2       5     1981
2       6     1982
2       8     1984
3       0     1984
3       2     1985
4       0     1980
4       20    1981
4       30    1982
4       30    1984
4       35    1985

This should produce 4 jagged lines on a plot, some shorter than others.

So far, I can see no simple equivalent of the $GRA instruction with the
factors but presumably the trick is to fill up a matrix with the data in a
rather ugly loop storing the row number and incrementing on a change in
Item.  Ensure that the matrix is NA-filled first and then use matplot to
do the graph.

So (a) is there an alternative and (b) is there a single assignment that
will copy the Size vector into a matrix of some sort?  The only way I can
see to do the latter is equally messy!

Sorry to bother - I have an antipathy to ugly coding where something
elegant will do!  Perhaps a coding therapist is in order?

\John

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