GNUPLOT : how to stop "histeps" from terminating to zero (y=0) at start and endpoints? - gnuplot

Question

I am using the following script for plotting data points from file "delete.dat"
set terminal jpeg
set output "delete_histeps.jpeg"
set title "with histeps"
plot "delete.dat" using 1:2 index 0 pt 7 ps 0.2 lc "black" notitle,\
"delete.dat" using 1:2 index 1 pt 7 ps 0.2 lc "red" notitle,\
"delete.dat" using 1:2 index 2 pt 7 ps 0.2 lc "green" notitle,\
"delete.dat" using 1:2 index 0 with histeps lc "black",\
"delete.dat" using 1:2 index 1 with histeps lc "red",\
"delete.dat" using 1:2 index 2 with histeps lc "green"
and the "delete.dat" file is
1 2
3 4
5 6
7 8
9 10
-1 5
-2 3
-3 4
-4 2
-5 6
5 1
6 2
7 3
8 4
9 5
10 4
11 3
12 12
But the start and end step is dropping to zero, which I don't want. Though for step and fsteps command, the steps begin (end) at the first (last) data point, without dropping down to zero (y=0). Can you please suggest that works like histeps (which keeps data points in the middle of the steps) but does not terminate to zero (like steps or fsteps). I'm also attaching pictures.

Answer 1

If your data points are equidistant (like the ones you provided), an alternative hack would be possible as well by combining fsteps and steps and shifting the x-value by half the point-to-point-distance:
plot "delete.dat" i 0 pt 7 ps 2 lc "black" not, \
'' i 1 pt 7 ps 2 lc "red" not, \
'' i 2 pt 7 ps 2 lc "green" not, \
'' u ($1-1.0):2 i 0 w steps lc "black", '' u ($1+1.0):2 i 0 w fsteps lc "black" not, \
'' u ($1+0.5):2 i 1 w steps lc "red", '' u ($1-0.5):2 i 1 w fsteps lc "red" not, \
'' u ($1-0.5):2 i 2 w steps lc "green", '' u ($1+0.5):2 i 2 w fsteps lc "green" not
The trick here is that steps or fsteps alone would miss either the last or the first point and the line would end in mid-air, therefore both have to be plotted on top of each other with the same plotting style.
One must take care of the correct sign: if x is positive, steps get a downshift and fsteps get an upshift; and vice-versa if x is negative.
My answer is definitely not as "robust" as the one of theozh, but maybe easier to understand.

Answer 2

Well, that's how hispteps, steps, and fsteps have been defined.
Then, you have to create your own steps. A solution could be the following:
Code: (improved version)
### steps like histeps but not dropping to zero
reset session
set colorsequence classic
$Data <<EOD
1 2
3 4
5 6
7 8
9 10
-1 5
-2 3
-3 4
-4 2
-5 6
5 1
6 2
7 3
8 4
9 5
10 4
11 3
12 12
EOD
set table $myStep
do for [i=0:2] {
plot $Data u ($0==0?(x1=x2=$1):(x1=x2,x2=$1),(c=$0,x1+x2)/2.):2 index i w table
plot $Data u 1:2 every ::c index i w table # add last value
plot '+' u ("") every ::::1 w table # add two empty lines
}
unset table
set key top left
plot for [i=0:2] $myStep u 1:2 index i w step lc i lw 3 notitle,\
for [i=0:2] $Data u 1:2 index i w p pt 7 lc i notitle, \
### end of code
Result: