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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>
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<h3>8.12.2: Ignoring columns that are not of interest</h3>
Quite often a dataset will have many columns, of which only a couple are
of interest to you. Consider for example oceanographic data which
has columns storing, in order, these variables: (1) depth in water
column, (2) "in situ" temperature, (3) "potential" temperature, (4)
salinity, (5) conductivity, (6) density, (7) sigma-theta, (8) sound
speed, and (9) oxygen concentration. But you might only be interested
in plotting a graph of salinity on the x-axis and depth on the y-axis.
Here are several ways to do this:
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<PRE>
<font color="#82140F">
open file
read columns y * * x
draw curve
</font></PRE>
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where the `<font color="#82140F"><code>*</code></font>' is a place-keeper to indicate to skip that column.
For a large number of columns, or as an aesthetic choice, you might
prefer to write this a
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<font color="#82140F">
open file
read columns y=1 x=4
draw curve
</font></PRE>
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<p>
Many users would just as soon not bother with this syntax, preferring
instead to use system tools with which they are more familiar. So a
Gawk user might write
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open "gawk '{print($1, $4)}' file |"
read columns y x
draw curve
</font></PRE>
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For more on the Gawk command see see <a href="SystemTools.html#Awk">Awk</a>.
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