Shell Programming and Scripting

1,1 1,2 1,3 1,4 1,5 1,6 1,7 1,8 1,9 1,10 
2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,9 2,10 
3,1 3,2 3,3 3,4 3,5 3,6 3,7 3,8 3,9 3,10 
4,1 4,2 4,3 4,4 4,5 4,6 4,7 4,8 4,9 4,10

 
1,6  1,10
2,6  2,10
3,6  3,10
4,6  4,10

 
1,1  1,4  1,7
2,1  2,4  2,7
3,1  3,4  3,7
4,1  4,4  4,7

/**
 *	rc.c	picks random columns from whitespace-separated input from stdin.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

const char ofs=' ';		// output field separator
const char *fs=" \r\n\t";	// input field seperator

int main(int argc, char *argv[])
{
	size_t size;	// buf[] size in bytes
	char *buf=malloc(size=65536L);
	int pos=0;	// How much's been read into buf[]

	int coln=0, colmax;	// How many columns read, max columns in cols[]
	char **cols=malloc(sizeof(char *) * (colmax=512L));

	int choose=1;	// How many columns to choose

	if(argc != 2)
	{
		fprintf(stderr, "Usage:  %s columns < datafile\n",argv[0]);
		return(1);
	}

	if((sscanf(argv[1], "%d", &choose) != 1) || (choose <= 0))
	{
		fprintf(stderr, "Bad count '%s'\n", argv[1]);
		return(1);
	}

	srand(time(NULL)^getpid());	// Make results random

	// Read until end of file
	while(fgets(buf+pos, size-pos, stdin) != NULL)
	{
		int c;
		char *tok;

		pos += strlen(buf+pos);// Find the end of line
		if(pos <= 0) continue; // Don't bother checking empty line
		// Check the end of line for \n
		if(buf[pos-1] != '\n')
		{	// Didn't get entire line, make buffer bigger
			// then get the rest
			buf=realloc(buf, size += size>>1);
			continue;
		}

		// Break into columns across whitespace
		tok=strtok(buf, fs);
		do
		{
			// Check if we have enough room for columns.
			// Add more if necessary.
			if(colmax <= coln)
				cols=realloc(cols, sizeof(char *)*
					(colmax+=(colmax>>1)));

			cols[coln++]=tok;
			tok=strtok(NULL, fs);
		} while(tok != NULL);

		for(c=0; (c<choose)&&(coln>0); c++)
		{
			int m=rand()%coln;
			char *pick=cols[m];
			cols[m]=cols[--coln];	// Remove from list

			if(c != 0)	putc(ofs, stdout);
			fputs(pick, stdout);
		}

		putc('\n', stdout);

		// Reset everything for next line
		coln=0;		pos=0;
	}

	return(0);
}

#!/usr/bin/env bash

# @(#) s1	Demonstrate extraction of random number of columns.

# Utility functions: print-as-echo, print-line-with-visual-space, debug.
pe() { for i;do printf "%s" "$i";done; printf "\n"; }
pl() { pe;pe "-----" ;pe "$*"; }
db() { ( printf " db, ";for i;do printf "%s" "$i";done; printf "\n" ) >&2 ; }
db() { : ; }
C=$HOME/bin/context && [ -f $C ] && . $C seq rl tr sed cut

N=${1-3}
FILE=data1

# Generate N numbers in random sequence, range 1 - number-of-columns
cols=$( seq 1 10 | rl -c $N | tr '\n' ',' | sed 's/.$//' )

pl " Random columns: $cols"

cut -d" " -f"$cols" $FILE

exit 0

% ./s1

Environment: LC_ALL = C, LANG = C
(Versions displayed with local utility "version")
OS, ker|rel, machine: Linux, 2.6.26-2-amd64, x86_64
Distribution        : Debian GNU/Linux 5.0.7 (lenny) 
GNU bash 3.2.39
seq (GNU coreutils) 6.10
rl 0.2.7
tr (GNU coreutils) 6.10
GNU sed version 4.1.5
cut (GNU coreutils) 6.10

-----
 Random columns: 7,9,2
1,2 1,7 1,9
2,2 2,7 2,9
3,2 3,7 3,9
4,2 4,7 4,9

% ./s1 5

... omitted

-----
 Random columns: 8,2,9,1,5
1,1 1,2 1,5 1,8 1,9
2,1 2,2 2,5 2,8 2,9
3,1 3,2 3,5 3,8 3,9
4,1 4,2 4,5 4,8 4,9