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<title>Gri: column algebra</title>
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Chapters:
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<a href="Introduction.html">1: Introduction</a><br>
<a href="SimpleExample.html">2: Simple example</a><br>
<a href="InvokingGri.html">3: Invocation</a><br>
<a href="GettingMoreControl.html">4: Finer Control</a><br>
<a href="X-Y.html">5: X-Y Plots</a><br>
<a href="ContourPlots.html">6: Contour Plots</a><br>
<a href="Images.html">7: Image Plots</a><br>
<a href="Examples.html">8: Examples</a><br>
<a href="Commands.html">9: Gri Commands</a><br>
<a href="Programming.html">10: Programming</a><br>
<a href="Environment.html">11: Environment</a><br>
<a href="Emacs.html">12: Emacs Mode</a><br>
<a href="History.html">13: History</a><br>
<a href="Installation.html">14: Installation</a><br>
<a href="Bugs.html">15: Gri Bugs</a><br>
<a href="TestSuite.html">16: Test Suite</a><br>
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<a href="Acknowledgments.html">18: Acknowledgments</a><br>
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Indices:<br>
<a href="ConceptIndex.html"><i>Concepts</i></a><br>
<a href="CommandIndex.html"><i>Commands</i></a><br>
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<h3>8.12.3: Algebra on column data</h3>
Suppose the file contains (x,y), but you wish to plot 2y times x. You
could do the doubling of y within Gri, as
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open file
read columns x y
y *= 2
draw curve
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or you could use a system tool, e.g. gawk, as in this example (see <a href="SystemTools.html#Awk">Awk</a>).
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open "gawk '{print($1,2*$2)}' file|"
read columns x y
draw curve
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The latter is preferable in the sense that it is more powerful. The
reason for this is that Gri allows you to manipulate the x and y
columns, using so-called RPN mathematics (see <a href="ReversePolishMath.html#rpnMathematics">rpn Mathematics</a>), but
you cannot blend the columns. For example, you cannot easily form the
ratio y/x in Gri. (Actually, you can, by looping through your data and
doing the calculation index by index, but if you knew that already you
wouldn't need to be reading this section!) Such blending is trivial in
the operating system, though, as in the following Gawk example (see <a href="SystemTools.html#Awk">Awk</a>).
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open "gawk 'print {($1, $2/$1)}' file |"
read columns x y
draw curve
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