Taking multiple header (rows matching condition) and convert into a column - bash

Question

Hello I have a file that has multiple Headers in it that I need to have turned into column values. The file looks like this:
Day1
1,Smith,London
2,Bruce,Seattle
5,Will,Dallas
Day2
1,Mike,Frisco
4,James,LA
I would like the file to end up looking like this:
Day1,1,Smith,London
Day1,2,Bruce,Seattle
Day1,5,Will,Dallas
Day2,1,Mike,Frisco
Day2,4,James,LA
The file doesn't have sequential numbers before the names and it doesn't have the same quantity of records after the "Day" Header.
Does anyone have any ideas on how to accomplish this using the command-line?

Answer 1

In awk
awk -F, 'NF==1{a=$0;next}{print a","$0}' file
Checks if the number of fields is 1, if it is it sets a variable to that and skips the next block.
For each line that doesn't have 1 field, it prints the saved variable and the line
And in sed
sed -n '/,/!{h};/,/{x;G;s/\n/,/;p;s/,.*//;x}' file
Broken down for MrBones wild ride.
sed -n '
/,/!{h}; // If the line does not contain a comma overwrite buffer with line
/,/{ // If the line contains a comma, do everything inside the brackets
x; // Exchange the line for the held in buffer
G; // Append buffer to line
s/\n/,/; // Replace the newline with a comma
p; // Print the line
s/,.*//; // Remove everything after the first comma
x // exchange line for hold buffer to put title back in buffer for the next line.
}' file // The file you are using
In essence it saves the lines without a ,, i.e the headers. Then if its not a header, it switches the current line with the saved header and appends the now switched line to the end of the header. As it is appended with a newline, then the next statement replaces that with a comma. Then the line is printed. NExt to recover the header, everything after it is removed and it is swapped back into the buffer, ready for the next line.

Answer 2

sed '/^Day/ {h;d;}
G;s/\(.*\)\n\(.*\)/\2,\1/
' YourFile
posix compliant
print nothing if not at least 1 data after a Day
white line are treated as data
awk '{if ( $0 ~ /^Day/ ) Head = $0; else print Head "," $0}' YourFile
use Day as paragraph separator and content as header to use on following line

Answer 3

Perl solution:
#! /usr/bin/perl
use warnings;
use strict;
my $header;
while (<>) { # Read line by line.
if (/,/) { # If the line contains a comma,
print "$header,$_"; # prepend the header.
} else {
chomp; # Remove the newline.
$header = $_; # Remember the header.
}
}

Answer 4

Another sed version
sed -n '/Day[0-9]\+/{h;b end};{G;s/\(.*\)\n\(.*\)/\2,\1/;p;:end}'

Answer 5

Perl
$ perl -F, -wlane ' if(#F eq 1){$s=$F[0]; next}print "$s,$_"' file
Day1,1,Smith,London
Day1,2,Bruce,Seattle
Day1,5,Will,Dallas
Day2,1,Mike,Frisco
Day2,4,James,LA

Answer 6

This Perl one-line program will do as you ask. It requires Perl v5.14 or better
perl -ne'tr/,// ? print $c,$_ : ($c = s/\s*\z/,/r)' myfile.txt
for earlier versions of perl, use
perl -ne'tr/,// ? print $c,$_ : ($c = $_) =~ s/\s*\z/,/' myfile.txt
output
Day1,1,Smith,London
Day1,2,Bruce,Seattle
Day1,5,Will,Dallas
Day2,1,Mike,Frisco
Day2,4,James,LA

Answer 7

Another perl example- this time using $/ to separate each record.
use strict;
use warnings;
local $/ = "Day";
while (<>) {
next unless my ($num) = m/^(\d+)/;
for ( split /\n/ ) {
print "Day${num},$_\n" if m/,/;
}
}