[GWM] Oct 2004 A simple canvas object to display a bar histogram from given data.

 global ready
 set ready 0
 proc histogram {slist wid ht} { ;# render a histogram
	global ready
	array set scores $slist
	set nms [lsort -integer [array names scores]]
	catch {destroy .h} {}
	catch {destroy .b} {}
	canvas .h -width $wid -height $ht -bg beige
  	pack .h
	set nbars [array size scores] ;#how many histogram bars
	set nax [expr $nbars/10] ;# axis spacing
	set hwid [expr $wid/ $nbars]
	set i 0
	set hmax -9999999 ;# largest y value 
	set hmin  9999999 ;# smallest y value
	while {$i<$nbars} {
		set f $scores([lindex $nms $i])
		set hmax [ expr {$f>$hmax} ? $f : $hmax]
		set hmin [ expr {$f<$hmin} ? $f : $hmin]
		incr i
	}

	if {$hmax>$hmin} {
	set i 0
	set nay 100
	while {$nay<$hmax} {
		set yp [expr $ht-0.75*$nay-20]
		.h create line  0 $yp $wid $yp -fill red
		incr nay 100
	}
	set nax 10
	while {$i<$nbars} {
		set x [expr $hwid*$i]
		set rhs [expr $x+$hwid/2]
		set f [expr $ht-20-.75*$ht*$scores([lindex $nms $i])/$hmax]
		.h create rectangle  $x [expr $ht-20] $rhs $f -fill gray
		if {[expr $i>=$nax]} {
		.h create line  $x [expr $ht-20] $x 0 -fill red
			incr nax 10
		}
		incr i
		incr x $hwid
	}
	update

	button .b  -text "Next" -command "incr ready" ;# when ready is changed, proceeds with commands
	pack .b
	}
 }

Call using
 histogram {1 2 2 3 3 5 4 7 5 6} 500 400

The list is actually an array = catgory 1 occurred twice; category 2 three times, category 5 6 times. For a way of looking at the rand function:
 for {set i 0} {$i<50} {incr i} {lappend scores $i [expr rand()]}
 histogram $scores 300 200

will show a histogram of the value returned by rand for 50 trials.

[Category Widget] [Category Mathematics]