How to use awk with a for loop?

Question

I have a 5 column file

2       649     2       82      1
3       651     1       83      1
2       652     3       84      2
...     ...     ...     ...     ...

The first column is n number of points in segment, the second is the x coordinate, the third is delta x, the delta between the current x coordinate and the next one, similarly the fourth column is the y coordinate and fifth is delta y. I need to generate all points in the segments so the output should be, from the data in the first line

649     82
650     82.5

From the data in the second line

651     83
651.33  83.33
651.67  83.67

From the data in the third line

652     84
653.5   85

Any idea How to do it?

You also need to explain how to arrive at that output from the input. Is it sorted? some other way? — P.P
– P.P, Commented Jun 8, 2014 at 20:11

P.P · Accepted Answer · 2014-06-08 20:34:40Z

2

This will do:

    awk '{n=$1; x=$2; dx=$3; y=$4; dy=$5;  \
    for(i=0;i<n;i++) printf "%.2f %.2f\n", x+i*dx/n, y+i*dy/n; }' file

You can adjust %.2f as you desired. For e.g. %.4f to print 4 digits of fraction.

I only used variables for clarity. Otherwise, you could simply do:

awk '{for(i=0;i<$1;i++) printf "%.2f %.2f\n", $2+i*$3/$1, $4+i*$5/$1; }' file

edited Jun 8, 2014 at 20:34

answered Jun 8, 2014 at 20:24

P.P

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7 Comments

e271p314 Over a year ago

Last question, I'd like to round the values so instead of printing 83.67 I'd like to print 84, how can I do it?

P.P Over a year ago

@e271p314 You mean ceil if fraction is more than .5 ? If so, you could do: awk '{for(i=0;i<$1;i++) printf "%d %d\n", $2+i*$3/$1+0.5, $4+i*$5/$1+0.5; }' file

e271p314 Over a year ago

Yes, ceil if more than .5 and floor otherwise

P.P Over a year ago

@e271p314 ceil is not an awk function. You could try this: awk '{for(i=0;i<$1;i++) printf "%d %d\n", $2+i*$3/$1+0.5, $4+i*$5/$1+0.5; }' file

P.P Over a year ago

There's no round or ceil function in awk. You could use this [round function[(gnu.org/software/gawk/manual/html_node/Round-Function.html) if you want. But I can't see why adding 0.5 won't work in all cases. Do you have any example where it'll fail?

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