Guide to Madagascar programs

sfheadersort: Sort a dataset according to a header key.

sfheadersort < in.rsf > out.rsf head=

string	head=		header file

sfheadersort is used to sort traces in the input file according to trace header information.

Here is an example of using sfheadersort for randomly shuffling traces in the input file. First, let us create an input file with seven traces:

bash$ sfmath n1=5 n2=7 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

Next, we can create a random file with seven header values using sfnoise.

bash$ sfspike n1=7 | sfnoise rep=y type=n > random.rsf
bash$ < random.rsf sfdisfil
   0:       0.05256      -0.2879       0.1487       0.4097       0.1548
   5:        0.4501       0.2836

If you reproduce this example, your numbers will most likely be different, because, in the absence of seed= parameter, sfnoise uses a random seed value to generate pseudo-random numbers. Finally, we apply sfheadersort to shuffle the input traces.

bash$ < input.rsf sfheadersort head=random.rsf > output.rsf
bash$ < output.rsf sfdisfil
   0:             2            2            2            2            2
   5:             1            1            1            1            1
  10:             3            3            3            3            3
  15:             5            5            5            5            5
  20:             7            7            7            7            7
  25:             4            4            4            4            4
  30:             6            6            6            6            6

As expected, the order of traces in the output file corresponds to the order of values in the header. Thanks to the separation between headers and data, the operation of sfheadersort is optimally efficient. It first sorts the headers and only then accesses the data, reading each data trace only once.

Guide to Madagascar programs