Plotting irregularly-spaced arrays in gnuplot 5.x - arrays

Question

gnuplot 5.x now supports arrays, but there seems to be no way to plot, or fit, to an irregularly-spaced set of data, if it is not provided in an external file. What I would like to see is the ability to plot "y vs x":
array z[8]=[0,1,2,3,4,5,6,6.4]
array f[8]=[0.468,0.405,0.342,0.279,0.216,0.153,0.090,0.064]
plot z,f
or even
plot [3,3],[0,0.25] w lines
which would, for example, provide a handy vertical marker line at x=3 without needing to resort to arrows without heads:
plot '+' using (3):(0):(0):(0.25) with vectors nohead
One can achieve the plotting in this awkward-looking way:
plot sample [j=1:|x|] '+' using (x[j]):(y[j])
but, unfortunately, the same syntax is not recognized by the fit command.
The only way I figured so far is to write the data to a virtual file (a data block), and use it as input to both plot and fit commands:
set print $DATA
print sprintf("# z\tf") ## header line, overwrite old content if any
set print $DATA append ## append data lines
do for [j=1:|z|] {
print sprintf("%f\t%f",z[j],f[j])
}
unset print
y(x)=m*x-y0
y0=0.25
m=1
fit y(x) $DATA via m,y0
plot $DATA t 'data',y(x) w lines t 'fit'
Is there a better way? Or can someone explain to me why such an obvious task is not a part of the standard plot/array implementation? It certainly would be one of the first things on my wish list.

Answer 1

What describe is exactly the purpose of data blocks:
$DATA <<EOD
0 0.468
1 0.405
2 0.342
3 0.279
4 0.216
5 0.153
6 0.090
6.4 0.064
EOD
y(x)=m*x-y0
y0=0.25
m=1
fit y(x) $DATA via m,y0
plot $DATA t 'data',y(x) w lines t 'fit'

Answer 2

Thanks Christoph for extensive help. It has emerged that data block syntax together with the appropriate "using" options would achieve what I had set out to do. Inline specification for a data block is perfectly compact, and the pre-processing can be replaced for both plot... and fit... with identical syntax:
$DATA <<EOD
0 0.468
1 0.405
2 0.342
3 0.279
4 0.216
5 0.153
6 0.090
6.4 0.064
EOD
y(x)=m*(x-x0)**2+y0
y0=0.9
m=-0.1
x0=4
fit y(x) $DATA using ($1):($1)*($2) via m,x0,y0
plot $DATA using ($1):($1)*($2) t 'data',y(x) w lines t 'fit'

Answer 3

To plot the data stored in arrays as it is, you can write it in the following way (I tried this in version 5.4).
array z[8]=[0,1,2,3,4,5,6,6.4]
array f[8]=[0.468,0.405,0.342,0.279,0.216,0.153,0.090,0.064]
plot z using (z[$0+1]):(f[$0+1])
At first glance, it seems that (z[$0+1]) in using can be replaced by 1, but in the version I tried, I had to do this.