A further question about calculating average "distance" between the corresponding content in two files.

Question

Now my program generates two data files. a.txt and b.txt Take a.txt as an example, it's content just like this:

0,0
0,1
1,0
-3,1
1,-2
1,3
......

b.txt is similar with a.txt.

Now, I hope to find out average distance between the corresponding content in a and b file. In other words, for example, if b.txt like this:

0,0
1,1
1,2
-3,1
1,-2
1,3
......

Then the distance is calculated in this way:

  sqrt[square(0-0)+square(0-0)]
    +sqrt[square(0-1)+square(1-1)]
    +sqrt[square(1-1)+square(0-2)]
    +sqrt[square((-3)-(-3))+square(1-1)]
    +sqrt[square(1-1)+square((-2)-(-2))]
    .......
   _____________
   /Total number(i.e 10,000)

to get the average distance between these two files content.

Question: how to write a shell script which can carry out the calculation process like above? And output the final average distance?

Hint: you may view two groups of coordinates are stored in two files.

Need your kind help..Many many Thanks.

Addition: There are about 10,000 - 100,000 rows for each files.

Answer 1

This would be much easier in a scripting language like perl or python. However in a shell script you would probably want to use:

• cut to split the files up
• bc to do the calculation
• whatever loop construct you prefer in your script language

I've left this vague in case it is homework.

Answer 2

AWK is really good for doing simple mathematical calculations on files containing rows of delimited data. There is a very good AWK guide here: http://www.vectorsite.net/tsawk.html

A general structure for this program could be:

Store the first row
For each additional row, calculate the distance between it and the last row and overwrite the stored values
Add the distance to a variable containing the distance sum
Divide at the end by the number of rows seen (conveniently stored for you by AWK)
Output the result