mjhjmtu

I have a file (comma separated) on a Linux system with 3 columns. I want to start new column after every 4th row.

Input:

col1,col2,col3 
1,disease1,high
1,disease2,low 
1,disease3,high
col1,col2,col3 
2,disease1,low 
2,disease2,low 
2,disease3,high
col1,col2,col3
3,disease1,low
3,disease2,low
3,disease3,low

Expected output:

col1,col2,col3,col1,col2,col3,col1,col2,col3
1,disease1,high,2,disease1,low,3,disease1,low
1,disease2,low,2,disease2,low,3,disease2,low
1,disease3,high,2,disease3,high,disease3,low

i.e. I want exactly 4 lines of output, each line is the result of joining every fourth line of the input with a comma.

With awk:

awk 'a[NR%4] = a[NR%4] (NR<=4 ? "" : ",") $0
 ENDfor (i = 1; i <= 4; i++) print a[i%4]' < input.txt

Try pasteing four lines into one, reading those into four variables, appending each to output lines:

paste -s -d" n" file | 
 while read A B C D 
 do L1="$L1$DL$A"
 L2="$L2$DL$B"
 L3="$L3$DL$C"
 L4="$L4$DL$D"
 DL=, 
 done 
 printf "%sn" "$L1" "$L2" "$L3" "$L4" 

col1,col2,col3,col1,col2,col3,
1,disease1,high,2,disease1,low,
1,disease2,low,2,disease2,low,
1,disease3,high,2,disease3,high,

EDIT: or, a bit simpler, no paste needed:

while read A && read B && read C && read D 
 do L1="$L1$DL$A"
 L2="$L2$DL$B"
 L3="$L3$DL$C"
 L4="$L4$DL$D"
 DL=, 
 done < file 
printf "%sn" "$L1" "$L2" "$L3" "$L4"