how to convert column with whitespace into multiple rows using awk

Question

I have a data file having few columns and there are white space after few data points. I want to convert 1st column into multiple rows (convert columns after whitespace into rows) .

e.g data file A.dat

    2    1  
   11    1  
   15    2  
   24    2  

    3    1  
   12    1  
   16    2  
   25    2  

    4    1  
   13    1  
   17    2  
   26    2  

using following command I am able to convert 1st column into Rows

awk '{print $1}' A.dat | awk 'BEGIN { ORS = " " } { print }'

this is the output of the above command

2 11 15 24  3 12 16 25  4 13 17 26

Requirements

I want my output like this

this is row: 2 11 15 24  
this is row: 3 12 16 25  
this is row: 4 13 17 26

Is it possible to convert column into rows with "this is row" in front of that using awk or any other way. I don't have much knowledge about other methods.

Answer 1

This may be what you're trying to do:

awk '
    NF        { row = row " " $1; next }
    row != "" { print "this is row:" row; row="" }
    END       { if (row != "") print "this is row:" row }
' A.dat

This assumes a blank line finishes the row and a non-blank line starts a new row.

Alternatively, using sed:

sed -e 's/[[:blank:]]*\([^[:blank:]]*\).*/\1/' \
    -e '/./{;H;$!d;}'                          \
    -e 'x;/^$/d;y/\n/ /;s/^/this is row:/'     \
A.dat