Select / Print odd-even elements of an array


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# 1  
Select / Print odd-even elements of an array

Hello experts,

I wish to print the contents of odd-even numbered indices of an array.

The problem statement is as follows :

1. The first line contains an integer, (the number of test cases).
2. Each line of the subsequent lines containing a string.

Example:

Code:
2
Haider
Bash


Explanation:

Code:
A[0]=H
A[1]=a
A[2]=i
A[3]=d
A[4]=e
A[5]=r


X[0]=B
X[1]=a
X[2]=s
X[3]=h


The expected output :

Hie adr :: The first elements are the even indexed elements are displayed followed by a space, followed by the odd indexed elements of array 1.
Bs ah :: The first elements are the even indexed elements are displayed followed by a space, followed by the odd indexed elements of array 2.

Code written so far :

Code:
read n
read -a arr1
read -a arr2

Could you please help.

Thanks,
Haider


Moderator's Comments:
Mod Comment Thanks for using code tags, but usually you don't have to put code tags inside code tags. I removed some to make it a bit more readable.

Last edited by zaxxon; 08-22-2016 at 02:59 AM..
# 2  
Hello H squared,

Following may help you in same.(tested with GNU awk).
Code:
awk '($0 ~ /[[:digit:]]/){print;next} ($0 ~ /[[:alpha:]]/){num=split($0, A,"");for(i=1;i<=num;i+=2){Q=Q?Q A[i]:A[i]};Q=Q OFS;for(i=2;i<=num;i+=2){Q=Q?Q A[i]:A[i]};print Q;Q=""}'  Input_file

Output will be as follows.
Code:
2
Hie adr
Bs ah

EDIT: Adding a non-one liner form of solution now.
Code:
awk '($0 ~ /[[:digit:]]/){
                                print;
                                next
                         }
     ($0 ~ /[[:alpha:]]/){
                                num=split($0, A,"");
                                for(i=1;i<=num;i+=2){
                                                        Q=Q?Q A[i]:A[i]
                                                    };
                                Q=Q OFS;
                                for(i=2;i<=num;i+=2){
                                                        Q=Q?Q A[i]:A[i]
                                                    };
                                print Q;
                                Q=""
                         }
    '   Input_file

EDIT2: Adding one more solution on same too.
Code:
awk '($0 ~ /[[:digit:]]/){print;next} ($0 ~ /[[:alpha:]]/){num=split($0, A,"");for(i=1;i<=num;i++){Q=i%2==0?(v1=v1?v1 A[i]:A[i]):(v2=v2?v2 A[i]:A[i])};print v2 OFS v1;v1=v2=""}'  Input_file

OR(non-one liner form of above solution)

awk '($0 ~ /[[:digit:]]/){
                                print;
                                next
                         }
     ($0 ~ /[[:alpha:]]/){
                                num=split($0, A,"");
                                for(i=1;i<=num;i++){
                                                        Q=i%2==0?(v1=v1?v1 A[i]:A[i]):(v2=v2?v2 A[i]:A[i])
                                                   };
                                print v2 OFS v1;
                                v1=v2=""
                         }
    '   Input_file

Output will be as follows.
Code:
2
Hie adr
Bs ah

Thanks,
R. Singh

Last edited by RavinderSingh13; 08-22-2016 at 03:31 AM.. Reason: Adding a non-one liner form of solution now. Added one more solution too now, to avoid 2 times loop running.
This User Gave Thanks to RavinderSingh13 For This Post:
# 3  
Try

Code:
[akshay@localhost tmp]$ cat f
2
Haider
Bash

Code:
[akshay@localhost tmp]$ awk '!/^[0-9]/{split($0,a,""); e=o="";for(i=1; i in a; i++) i%2?e=e a[i]:o=o a[i]; print e,o }' f
Hie adr
Bs ah

This User Gave Thanks to Akshay Hegde For This Post:
# 4  
Hi H squared,
That isn't the way arrays work. Reading an array creates elements based on field splitting; not arrays of individual characters. But, both recent versions of bash and 1993 or later versions of ksh support extensions to the standard providing simplified for loops and substring variable expansions that do what is needed here:
Code:
#!/bin/bash
{	read -r n
	printf 'Expecting to process %s lines...\n' "$n"
	while IFS= read -r text
	do	printf 'Processing text: "%s"\n' "$text"
		for((i = 0; i < ${#text}; i += 2))
		do	printf '%s' "${text:$i:1}"
		done
		printf ' '
		for((i = 1; i < ${#text}; i += 2))
		do	printf '%s' "${text:$i:1}"
		done
		echo
	done
} < file

which with the input you showed us in a file named file produces the output:
Code:
Expecting to process 2 lines..
Processing text: "Haider"
Hie adr
Processing text: "Bash"
Bs ah

This User Gave Thanks to Don Cragun For This Post:
# 5  
Code:
bash-3.2$ cat a.txt
Testing
Hello
What are you doing

bash-3.2$ awk 'BEGIN{FS=""}{for(i=1;i<=NF;i++)if(i%2){odd=odd$i}else{even=even$i}print odd,even;odd=even="";}' a.txt
Tsig etn
Hlo el
Wa r o on htaeyudig

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