Essays/Unicode Histogram

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Unicode Histogram

Information.png Illustrates these techniques:
  • Use of special unicode code points to make a simple histogram
  • A cheap 'n' cheerful character-only animation using the IJX window
  • Implementing a moderately accurate delay for J602 JWD (Macintosh).

On the Macintosh (j602a_mac_intel.dmg) 6!:3 delays only in multiples of one second.

Unicode has a set of code points (aka "characters") for building a crude histogram:

u: 16b2588	NB. U+2588 (9608) █	1.0	-start of horiz bar
u: 16b2589	NB. U+2589 (9609) ▉	.875
u: 16b258a	NB. U+258a (9610) ▊	.75
u: 16b258b	NB. U+258b (9611) ▋	.625
u: 16b258c	NB. U+258c (9612) ▌	.5
u: 16b258d	NB. U+258d (9613) ▍	.375
u: 16b258e	NB. U+258e (9614) ▎	.25
u: 16b258f	NB. U+258f (9615) ▏	.125

These block characters appear best when using the font "APL385 Unicode" (provided here by courtesy of the British APL Association):

Click to download font: APL385 Unicode

Some common non-proportional fonts like "Courier" and "Courier New" haven't designed them correctly.

Notice that these code points divide the basic block (U+2588) into eights, not tenths!

Information.png Unicode code points (see: [1])


are conventionally represented as U+xxxx where xxxx is a hex numeral
eg. U+2588.
This hex numeral can be expressed in J602 as: 16b2588
but in practice we will employ the corresponding decimal numeral, viz. 9608.

We can display the histogram for the number 3.4 (say) by means of 3 whole blocks (U+2588) followed by one of the partial blocks, U+258d being the closest fractional part (0.375) to 0.4:

   16b2588 16b2588 16b2588 16b258d
9608 9608 9608 9613

   u: 9608 9608 9608
███
   u: 9608 9608 9608 9608
████
   u: 9608 9608 9608 9613
███▍

But how do we compute the fractional part for any given real number?

The following demo shows how:

NB. Demo using unicode to display a histogram / progress bar

fh=: 9608 + [: >. 7.5 - 8 * ]
hst=: (9608 #~ <.) , 9616 -.~ [: fh ] - <.

delay=: 3 : 0
	NB. dynamic wait for y seconds
if. y-: 0 do. return. end.
if. IFWIN do. 6!:3 y
else.
  t1=. (|y) + t=. 6!:1''
  while. t<t1 do. t=. 6!:1'' end.
  i.0 0
end.
)

smclear=: 3 : 0
	NB. clear (/refill) the IJX session
	NB. y must be '' or LF-separated
try.
  if. IFIJX_0_ do.	NB. provided locale 0 is ijx...
    wd 'psel ',SMHWNDP_0_
    if. 0<#y do.
      wd 'set e *',LF ,~ y
    else.
      wd 'set e ""'
    end.
  else. @@		NB. force an error
  end.
catch.
  smoutput 'smclear: >>>cannot identify J session window'
end.
)

th=: 3 : 0
	NB. run the animated histogram for (y) frames
for_i. 10 %~ i.y do.
  smclear''
  smoutput (5j1 ": i) , TAB , u: hst i
  delay 0.1
end.
)

th 101

See the verb fh (=fractional-histogram), which is used in the verb hst, which outputs the whole histogram as a string of integers specifying unicode characters.

Thus, taking our earlier example, displaying the histogram for 3.4:

   hst 3.4
9608 9608 9608 9613
   u: hst 3.4
███▍

Possible uses:

  • Embedding mini-histograms in a grid or table of figures
  • Implementing a progress bar

Contributed by Ian Clark