awk/sed/bash to merge/concatenate data

Question

Trying to merge some data that I have. The input would look like so:

foo bar
foo baz boo
abc def
abc ghi

And I would like the output to look like:

foo bar baz boo
abc def ghi

I have some ideas using some arrays in a shell script, but I was looking for a more elegant or quicker solution.

Answer 1

if the length of the first field is fixed, you can use uniq with the -w option. Otherwise you night want to use awk (warning: untested code):

awk '
    BEGIN{last='';}
    {
        if ($1==last) {
            for (i = 1; i < NF;i++) print $i;
        } else {
            print "\n", $0;
            last = $1;
        }
    }'

Answer 2

How about join?

file="file"
join -a1 -a2 <(sort "$file" | sed -n 1~2p) <(sort "$file" | sed -n 2~2p)

The seds there are just splitting the file on odd and even lines

Answer 3

While pixelbeat's answer works, I can't say I'm very enthused about it. I think I'd use awk something like this:

    { for (i=2; i<=NF; i++) { lines[$1] = lines[$1] " " $i;} }  
END { for (i in lines) printf("%s%s\n", i, lines[i]); }

This shouldn't require pre-sorting the data, and should work fine regardless of the number or length of the fields (short of overflowing memory, of course). Its only obvious shortcoming is that its output is in an arbitrary order. If you need it sorted, you'll need to pipe the output through sort (but getting back to the original order would be something else).

Answer 4

An awk solution

awk '
    {key=$1; $1=""; x[key] = x[key] $0}
    END {for (key in x) {print key x[key]}}
' filename

Answer 5

Pure Bash, for truly alternating lines:

infile="paste.dat"

toggle=0
while read -a line ; do
  if [ $toggle -eq 0 ] ; then
    echo -n "${line[@]}"
  else
    unset line[0]               # remove first element
    echo  " ${line[@]}"
  fi
  ((toggle=1-toggle))
done < "$infile"

Answer 6

Based on fgm's pure Bash snippet:

text='
foo bar
foo baz boo
abc def
abc ghi
'

count=0
oneline=""
firstword=""
while IFS=" " read -a line ; do
   let count++
   if [[ $count -eq 1 ]]; then
      firstword="${line[0]}"
      oneline="${line[@]}"
   else
      if [[ "$firstword" == "${line[0]}" ]]; then
         unset line[0] # remove first word of line
         oneline="${oneline} ${line[@]}"
      else
         printf "%s\n" "${oneline}"
         oneline="${line[@]}"
         firstword="${line[0]}"
      fi
  fi
done <<< "$text"