[David H. Bigelow] wrote in [the comp.lang.tcl newsgroup]: The thing to remember with the Tcl Canvas widget is that it starts it's 0 0 at the upper left corner of your display and works down. Knowing that you are looking to do a graph. I have compensated for this so that the graph information is translated to the lower left corner and builds to the right. Here is the point data I used in a file called: data.txt 0,0 10,10 15,7.5 20,25 25,60 30,30 35,40 40,45 50,60 I have included a couple of variations for computing this. Both are computing the graph such that the origin is the lower left corner of the canvas -- so it looks like a graph: #**** PROGRAM 1 -- SIMPLE -- individual lines # DECLARE THE SIZE OF THE CANVAS set width 100 set height 100 canvas .c -width $width -height $height -background yellow pack .c # READ THE DATA FILE set infile [open data.txt] set indata [read $infile] close $infile set count 0 foreach point $indata { if {$count == 0} { set oldx [lindex [split $point ,] 0] set oldy [expr $height-[lindex [split $point ,] 1]] incr count } if {$count > 0} { set newx [lindex [split $point ,] 0] set newy [expr $height-[lindex [split $point ,] 1]] .c create line $oldx $oldy $newx $newy set oldx $newx set oldy $newy } } PROGRAM 1 is a very simple program to follow, and it gets the job done, although not as efficient as other methods (see below). However, if you are a beginner - this will plot data and quickly. Believe me -- there are more efficient methods. ---- #**** PROGRAM 2-- MEDIUM/COMPLEX -- Single line for same data # DECLARE THE SIZE OF THE CANVAS set width 100 set height 100 canvas .c -width $width -height $height -background yellow pack .c # READ THE DATA FILE set infile [open data.txt] set indata [read $infile] close $infile set linecoords {} foreach point $indata { set x [lindex [split $point ,] 0] set y [expr $height-[lindex [split $point ,] 1]] lappend linecoords $x $y } set test ".c create line [join $linecoords]" eval $test PROGRAM 2 is more complicated because it uses more advanved functions of Tcl than the first program. The advantage is that your data set is described in one element. Which may be very helpful if you have multiple data sets to deal with. ---- RS: Here are some things I'd do differently, just for discussion: * ''linecoords'' is a list, so it's slightly more efficient to initialize it as such * splitting the $point is done twice, once is enough * accessing with lindex is OK, but for constant positions, I prefer ''[foreach]...break'' * join is not needed, a list referenced in a string will come joined with spaces set linecoords [list] foreach point $indata { foreach {x y} [split $point ,] break lappend linecoords $x [expr {$height-$y}] } eval .c create line $linecoords ---- SB 2002-10-27: I wanted to be able to plot comma-separated data with one x-value and one or more y-values where spaces basically are ignored so that I can use either csv data from excel or hand-crafted csv files manually modified for human readability. This work is based on the above examples. The data file ''data.txt'': 0 ,0 ,1 ,56 ,0 10 ,10 ,5 ,70 ,10 15 ,7.5 ,7 ,65 ,15 20 ,25 ,9 ,10 ,20 25 ,60 ,19 ,4 ,25 30 ,30 ,12 ,3 ,30 35 ,40 ,56 ,16 ,35 40 ,45 ,12 ,45 ,40 50 ,60 ,34 ,22 ,50 60 ,45 ,17 ,23 ,60 70 ,10 ,15 ,50 ,70 The program: #**** PROGRAM 4-- COMPLEX # # DECLARE THE SIZE OF THE CANVAS set width 100 set height 100 canvas .c -width $width -height $height -background white pack .c # READ THE DATA FILE set infile [open "data.txt"] # knowing that this way of reading a file may be bad # I do it anyway and duck for cover while {[gets $infile indata] > -1} { set i 0 set el [split $indata ,] # looking for something like car and cdr from lisp to process the el list foreach {x yvals} [list [lindex $el 0] [lrange $el 1 end]] break # process each y-value, the lists are not initialized anymore # as I don't know how many datasets I have foreach y $yvals { lappend linecoords($i) $x [expr {$height-$y}] incr i } } close $infile # set some colors to be able to separate out each graph array set color { 0 black 1 red 2 blue 3 magenta } for {set n 0} {$n < $i} {incr n} { eval .c create line $linecoords($n) -fill $color($n) } SB 2002-11-23: For some reason the eval statement in the for line above dissapeared. Happened after the wiki started using css. Turned out to be one tab only in front. Replaced with spaces and the line shows again. ---- SB 2002-11-23: Now what happens if there are holes in a data range? In PROGRAM 4 this would lead to an error. The next example fix this. Additionally I have introduced strips: Instead of drawing all curves into one canvas, one canvas is created for each curve and then packed. This works well for few stripes, and an improvement will be a part of the next release. First the data file ''data2.txt'' 0 ,0 ,1 ,56 ,0 10 ,10 ,5 ,70 ,10 15 ,7.5 ,7 ,65 ,15 20 ,25 ,9 ,10 ,20 25 ,60 ,19 ,4 ,25 30 ,30 ,12 ,3 ,30 35 ,40 ,56 ,16 ,35 40 ,45 ,12 ,45 ,40 50 ,60 ,34 ,22 ,50 60 ,45 ,17 ,23 ,60 70 ,10 ,15 ,50 ,70 80 , , ,70 ,80 90 ,7.5 ,30 , , 100,8 ,20 ,30 ,0 The program: #**** PROGRAM 5 -- COMPLEX -- y-data may be missing, strips. # # DECLARE THE SIZE OF THE CANVAS set width 100 set height 100 # READ THE DATA FILE set infile [open "data2.txt"] while {[gets $infile indata] > -1} { set i 0 set el [split $indata ,] foreach {x yvals} [list [lindex $el 0] [lrange $el 1 end]] break # Adding check for empty y-values the bash way foreach y $yvals { if {[string trim "X$y"] != "X"} { lappend linecoords($i) $x [expr {$height-$y}] } incr i } } close $infile # set some colors to be able to separate out each graph array set color { 0 black 1 red 2 blue 3 magenta } # Now each run through loop create and pack a separate canvas for each curve for {set n 0} {$n < $i} {incr n} { canvas .c$n -width $width -height $height -background white eval .c$n create line $linecoords($n) -fill $color($n) pack .c$n } ---- [Arts and crafts of Tcl-Tk programming] - See also [A little function plotter] | [Category Application] | [Category Graphics]