Docstrings updated

docs/src/advanced.md

@@ -1,6 +1,45 @@
 # Advanced techniques
 
+Here we will show a few advanced techniques for data visualization using **Gnuplot.jl**.  The new concepts introduced in the examples are as follows:
+
+- a name can be associated to a dataset, in order to use it multiple times in a plot while sending it only once to gnuplot. A dataset name must begin with a `$`;
+
+- gnuplot is able to generate multiplot, i.e. a single figure containing multiple plots.  Each plot is identified by a numeric ID, starting from 1;
+
+- **Gnuplot.jl** is able to handle multiple sessions, i.e. multiple gnuplot processes running simultaneously.  Each session is identified by a symbol.  If the session ID is not specified the `:default` session is considered.
+
+
+```@setup abc
+using Gnuplot
+Gnuplot.quitall()
+mkpath("assets")
+saveas(file) = save(term="pngcairo size 480,360", output="assets/$(file).png")
+empty!(Gnuplot.options.init)
+Gnuplot.exec("set term unknown")
+```
+
+
+## Named datasets
+A named dataset can be used multiple times in a plot, avoiding sending to gnuplot the same data multiple times.  A dataset name must always start with a `$`, and the dataset is defined as a `Pair{String, Tuple}`, e.g.:
+```julia
+"\$name" => (1:10,)
+```
+
+A named dataset can be used as an argument to both `@gp` and `gsp`, e.g.:
+```@example abc
+x = range(-2pi, stop=2pi, length=100);
+y = sin.(x)
+name = "\$MyDataSet1"
+@gp name=>(x, y) "plot $name w l lc rgb 'black'" "pl $name u 1:(-1.5*\$2) w l lc rgb 'red'"
+saveas("ex010") # hide
+```
+![](assets/ex010.png)
+
+Both curves use the same input data, but the red curve has the second column (`\$2`, corresponding to the *y* value) is multiplied by a factor -1.5.
+
+
 ## Multiplot
+
 ### Mixing 2D and 3D plots
 ```julia
 
@@ -27,7 +66,6 @@ img = testimage("earth_apollo17");
 ```
 
 ## Multiple sessions
-## Named datasets
 ## Histograms (1D)
 ## Histograms (2D)
 ## Contour lines

docs/src/basic.md

@@ -29,7 +29,7 @@ before running the examples.
 ```@setup abc
 using Gnuplot
 Gnuplot.quitall()
-mkdir("assets")
+mkpath("assets")
 Gnuplot.splash("assets/logo.png")
 saveas(file) = save(term="pngcairo size 480,360", output="assets/$(file).png")
 empty!(Gnuplot.options.init)
@@ -44,17 +44,17 @@ Gnuplot.exec("set term unknown")
 #### Plot a sinusoid:
 ```@example abc
 @gp "plot sin(x)"
-saveas("basic1") # hide
+saveas("ex001") # hide
 ```
-![](assets/basic1.png)
+![](assets/ex001.png)
 
 ---
 #### Plot two curves:
 ```@example abc
 @gp "set key left" "plot sin(x)" "pl cos(x)"
-saveas("basic2") # hide
+saveas("ex002") # hide
 ```
-![](assets/basic2.png)
+![](assets/ex002.png)
 
 !!! note
     Note that all gnuplot commands can be abbreviated as long as the resulting string is not ambiguous.  In the example above we used `pl` in place of `plot`.
@@ -65,9 +65,9 @@ saveas("basic2") # hide
 @gp    "set grid"  :-
 @gp :- "p sin(x)"  :-
 @gp :- "plo cos(x)"
-saveas("basic3") # hide
+saveas("ex003") # hide
 ```
-![](assets/basic3.png)
+![](assets/ex003.png)
 
 
 ### Send data from Julia to gnuplot:
@@ -75,9 +75,9 @@ saveas("basic3") # hide
 #### Plot a parabola
 ```@example abc
 @gp (1:20).^2
-saveas("basic4") # hide
+saveas("ex004") # hide
 ```
-![](assets/basic4.png)
+![](assets/ex004.png)
 
 
 ---
@@ -85,9 +85,9 @@ saveas("basic4") # hide
 ```@example abc
 x = 1:20
 @gp "set key left"   x ./ 20   x.^2   "with lines tit 'Parabola'"
-saveas("basic5") # hide
+saveas("ex005") # hide
 ```
-![](assets/basic5.png)
+![](assets/ex005.png)
 
 ---
 #### Multiple datasets, logarithmic axis, labels and colors, etc.
@@ -98,9 +98,9 @@ x = 1:0.1:10
 @gp :- x x.^0.5 "w l tit 'Pow 0.5' dt 2 lw 2 lc rgb 'red'"
 @gp :- x x      "w l tit 'Pow 1'   dt 1 lw 3 lc rgb 'blue'"
 @gp :- x x.^2   "w l tit 'Pow 2'   dt 3 lw 2 lc rgb 'purple'"
-saveas("basic6") # hide
+saveas("ex006") # hide
 ```
-![](assets/basic6.png)
+![](assets/ex006.png)
 
 !!! note
     The above example lacks the trailing `:-` symbol.  This means the plot will be updated at each command, adding one curve at a time.
@@ -143,9 +143,9 @@ where `NaN` in the `xrange` keyword means using axis autoscaling.
 img = randn(Float64, 30, 50)
 img[10,:] .= -5
 @gp img "w image notit"
-saveas("basic7a") # hide
+saveas("ex007a") # hide
 ```
-![](assets/basic7a.png)
+![](assets/ex007a.png)
 
 Note that the first index in the `img` matrix corresponds to the `x` coordinate when the image is displayed.
 
@@ -154,18 +154,18 @@ If the orientation is not the correct one you may adjust it with the gnuplot `ro
 using TestImages
 img = testimage("lighthouse");
 @gp "set size square" "set autoscale fix" img "rotate=-90deg with rgbimage notit"
-save(term="jpeg size 480,360", output="assets/basic7b.jpg") # hide
+save(term="jpeg size 480,360", output="assets/ex007b.jpg") # hide
 ```
-![](assets/basic7b.jpg)
+![](assets/ex007b.jpg)
 
 
 To display a gray image use `with image` in place of `with rgbimage`, e.g.:
 ```@example abc
 img = testimage("walkbridge");
 @gp palette(:lapaz) "set size square" "set autoscale fix" img "rotate=-0.5pi with image notit"
-save(term="jpeg size 480,360", output="assets/basic7c.jpg") # hide
+save(term="jpeg size 480,360", output="assets/ex007c.jpg") # hide
 ```
-![](assets/basic7c.jpg)
+![](assets/ex007c.jpg)
 
 Note that we used a custom palette (`:lapaz`, see [Palettes and line types](@ref)) and the rotation angle has been expressed in radians (`-0.5pi`).
 
@@ -178,9 +178,9 @@ E.g., to plot a spiral increasing in size along the `X` direction:
 ```@example abc
 x = 0:0.1:10pi
 @gsp cbr=[-1,1].*30  x  sin.(x) .* x  cos.(x) .* x  x./20  "w p pt 7 ps var lc pal"
-saveas("basic8") # hide
+saveas("ex008") # hide
 ```
-![](assets/basic8.png)
+![](assets/ex008.png)
 
 Note that the fourth array in the dataset, `x./20`, is used as by gnuplot as point size (`ps var`).  Also note that all the keywords discussed above can also be used in 3D plots.
 
@@ -191,9 +191,9 @@ A gnuplot-compliant palette can be retrieved with `palette()`, and used as any o
 ```@example abc
 x = 0:0.1:10pi
 @gsp palette(:viridis) cbr=[-1,1].*30  x  sin.(x) .* x  cos.(x) .* x  x./20  "w p pt 7 ps var lc pal"
-saveas("basic8a") # hide
+saveas("ex008a") # hide
 ```
-![](assets/basic8a.png)
+![](assets/ex008a.png)
 
 
 The [ColorSchemes](https://juliagraphics.github.io/ColorSchemes.jl/stable/basics/#Pre-defined-schemes-1) palettes can also be used to generate line types (actually just line colors), by means of the `linetypes()` function, e.g.
@@ -203,9 +203,9 @@ x = 1:0.1:4pi
 for i in 1:5
     @gp :- x i.* sin.(x) "w l notit lw 5"
 end
-saveas("basic9") # hide
+saveas("ex009") # hide
 ```
-![](assets/basic9.png)
+![](assets/ex009.png)
 
 
 

src/Gnuplot.jl

@@ -1084,7 +1084,9 @@ The `@gp` macro, and its companion `@gsp` for 3D plots, allows to send data and
 
 - any other symbol is interpreted as a session ID;
 
-- an `Int` (> 0) is interpreted as the plot destination in a multi-plot session (this specification applies to subsequent arguments, not previous ones);
+- an `Int` (>= 1) is interpreted as the plot destination in a multi-plot session (this specification applies to subsequent arguments, not previous ones);
+
+- an input in the form `"\\\$name"=>(array1, array2, etc...)` is interpreted as a named dataset.  Note that the dataset name must always start with a "`\$`";
 
 - an input in the form `keyword=value` is interpreted as a keyword/value pair.  The accepted keywords and their corresponding *gnuplot* commands are as follows:
   - `xrange=[low, high]` => `"set xrange [low:high]`;
@@ -1099,9 +1101,7 @@ The `@gp` macro, and its companion `@gsp` for 3D plots, allows to send data and
   - `xlog=true`   => `set logscale x`;
   - `ylog=true`   => `set logscale y`;
   - `zlog=true`   => `set logscale z`.
-All Keyword names can be abbreviated as long as the resulting name is unambiguous.  E.g. you can use `xr=[1,10]` in place of `xrange=[1,10]`;
-
-- an input in the form `"name"=>(array1, array2, etc...)` is interpreted as a named dataset.
+All Keyword names can be abbreviated as long as the resulting name is unambiguous.  E.g. you can use `xr=[1,10]` in place of `xrange=[1,10]`.
 """
 macro gp(args...)
     out = Expr(:call)