Description

Each line begins with a tag separated with other contents by at least one space. The datafile can be divided into several groups where lines of a group begin with the same tag. The job is printing the last line of every group.

Raw Input		Desired Output
John 12 John 13 John 14 Mary 100 Mary 102 Kelly 55 Kelly 56 Kelly 57 Olivier 99		John 14 Mary 102 Kelly 57 Olivier 99

Script and Comments

Script₁

[ 1] 1h
[ 2] x
[ 3] G
[ 4] /^\([^ ]*\) .*\n\1 /!P
[ 5] $!d
[ 6] x

Comments

Pattern Space and Hold Space are abbreviated to PS and HS, respectively.
We use the HS to keep the previous line.
Step [1] is used to initialize the HS.
Step [2] is used to exchange the contents of PS and HS.
After Step [3], PS contains
Previous line \n Current line
In Step [4], if the current and previous line do not begin with the same tag, then command 'P' will print the previous line.
Now HS contains the current line, which can be used in the next cycle.
If the current line is not the last one of datafile, Step [5] will start next cycle; otherwise, the current line will be put back to PS by Step [6] and will be printed when this script is terminated.