Editing Guide to madagascar programs (section)

==sfheaderwindow==
{| class="wikitable" align="center" cellspacing="0" border="1"
! colspan="4" style="background:#ffdead;" | Window a dataset based on a header mask.
|-
! colspan="4" | sfheaderwindow mask=head.rsf < in.rsf > out.rsf inv=n
|-
|  colspan="4" | <br>The input data is a collection of traces n1xn2,<br>mask is an integer array os size n2, windowed is n1xm2,<br>where m2 is the number of nonzero elements in mask.
|-
| ''bool   '' || '''inv=n''' ||  [y/n] || 	inversion flag
|-
| ''file   '' || '''mask=''' ||   || 	auxiliary input file name
|}


<tt>sfheaderwindow</tt> is used to window traces in the input file
according to trace header information. 
Here is an example of using <tt>sfheaderwindow</tt> for randomly
selecting part of the traces in the input file. First, let us create
an input file with ten traces:
<pre>
bash$ sfmath n1=5 n2=10 output=x2+1 > input.rsf
bash$ < input.rsf sfdisfil
   0:             1            1            1            1            1
   5:             2            2            2            2            2
  10:             3            3            3            3            3
  15:             4            4            4            4            4
  20:             5            5            5            5            5
  25:             6            6            6            6            6
  30:             7            7            7            7            7
  35:             8            8            8            8            8
  40:             9            9            9            9            9
  45:            10           10           10           10           10
</pre>
Next, we can create a random file with ten header values using
<tt>sfnoise</tt>.
<pre>
bash$ sfspike n1=10 | sfnoise rep=y type=n > random.rsf
bash$ < random.rsf sfdisfil
   0:     -0.005768      0.02258     -0.04331      -0.4129      -0.3909
   5:      -0.03582       0.4595      -0.3326        0.498      -0.3517
</pre>
If you reproduce this example, your numbers will most likely be different,
because, in the absence of <tt>seed=</tt> parameter, <tt>sfnoise</tt>
uses a random seed value to generate pseudo-random numbers. Finally,
we apply <tt>sfheaderwindow</tt> to window the input traces selecting
only those for which the header is greater than zero.
<pre>
bash$ < random.rsf sfmask min=0 > mask.rsf
bash$ < mask.rsf sfdisfil
   0:    0    1    0    0    0    0    1    0    1    0
bash$ < input.rsf sfheaderwindow mask=mask.rsf > output.rsf
bash$ < output.rsf sfdisfil
   0:             2            2            2            2            2
   5:             7            7            7            7            7
  10:             9            9            9            9            9
</pre>
In this case, only three traces are selected for the output. Thanks to
the separation between headers and data, the operation of
<tt>sfheaderwindow</tt> is optimally efficient.