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  • 26 — Creating Graphs with grap

    • 26 — Creating Graphs with grap

      By Susan Peppard

      What is grap?

      grap is a troff preprocessor that uses pic to construct different types of graphs. Its use in data analysis is limited. For example, you can use grap to determine whether a population is growing exponentially. grap, then, is used primarily to include graphs in troff documents. Like the other troff preprocessors, it is fussy about syntax. You can't simply sit down and toss off three or four complicated graphs. You have to read the documentation. grap, like pic, faces stiff competition from the PC-based packages.

      NOTE: grap does not provide color or shading.

      The Basics

      One of the more endearing qualities of UNIX is its inconsistency. You would expect the grap macros to be .GS and .GE, and you would be wrong. The grap macros are .G1 and .G2. In addition to these macros, all that grap requires for a primitive graph is some data. Take, for example, the grades on a test:


      These dismal grades, after sorting, produce a scatter point graph.

      Because grap has a copy facility similar to that of pic, you can simplify your code even more by putting the data in a separate file. (See Chapter 25.) For example,

      copy "test.scores"

      If you want the graph to have a solid line instead of scatter points, simply add a line of code that says draw solid immediately after the .G1 macro.

      Adding Bells, Whistles, and Ticks

      You can make your graph much more attractive by drawing a frame, adding labels, and specifying ticks. The following code, for example, produces a more sophisticated graph.

      frame invis ht 2 wid 3 left solid bot solid
      label left "1990" "Dollars" left .5
      label bot "Grand Total:  $210,000"
      ticks left out at 6000 "6,000", 9000 "9,000", 12000 "12,000", 15000 "15,000",\
      18000 "18,000", 21000 "21,000"
      ticks bot at 1990 "1990", 1995 "1995", 2000 "2000", 2005 "2005", \
      2010 "2010"
      draw solid
      copy "cost.child"

      Here, the frame is shown only on the bottom and left side. The x and y coordinates have labels. Also, the ticks have been specified explicitly; they are not determined by grap.

      TIP: You can save yourself hours of debugging if you remember that grap doesn't understand commas in large numbers. The ticks left line above specifies 9000 "9,000". The commas are safely isolated in labels specified in quotation marks. The grap specifications themselves contain no commas.

      The data file—in this case, cost.child—also must contain no commas.

      NOTE: Earlier versions of grap may not recognize the abbreviation bot for bottom.

      You can specify ticks as out. This means that the ticks themselves, but not their labels, appear outside the grap frame. You can also specify ticks as in, in which case they appear inside the frame.

      If there are too many dates to fit across the bottom of a graph, you might want to use apostrophes in the labels, as in '10, '20, and '30. To do this, you must tell grap that your label is a literal. (This is what C programmers have to do all the time.) If you want to specify the first and last dates in full, you need to use two tick lines. The following code, for example, produces bottom labels of 1900, '05, '10, '15, and so on, up to 1950:

      ticks bottom out at 0 "1900", 50 "1950"
      ticks bottom out from 05 to 45 by 5 "'%g"

      NOTE: To suppress tick labels, use a null argument ("").

      Notice the words at 0 in the previous example. grap recognizes x,y coordinates, and unlike pic, it understands that 0,0 is the intersection of the x and y axes. To use coordinates, you use the coord command, as in

      coord x first-value, y last-value

      Without the coord command, grap automatically pads your first and last values, giving you blank space at the beginning and at the end of your graph. coord suppresses padding.

      Likewise, use coord if you want an exponential graph rather than a linear graph.

      You can plot the figures for low-income and high-income families on the graph shown in Figure 26.1.

      Figure 26.1. The cost of raising a child, by income level.

      The following code produced Figure 26.1.

      frame invis ht 2 wid 3 left solid bottom solid
      label left "1990" " Dollars" left .4
      "High" ljust at 2008,27000
      "Middle" ljust at 2008,20000
      "Low" ljust at 2008,14000
      ticks left out at 3000 "3,000", 6000 "6,000",\
      9000 "9,000", 12000 "12,000", 15000 "15,000",\
      18000 "18,000", 21000 "21,000", 24000 "24,000",\27000 "27,000", 30000 "30,000"
      ticks bottom at 1990 "1990", 1995 "1995", 2000 "2000", 2005 "2005", 2010 "2010"
      copy "cost2.child"
      draw dotted
      copy "cost.child"
      new solid
      copy "cost3.child"
      new dashed

      The data file is formatted like this:

      1990     4330
      1991     4590
      1992     4870
      1993     5510
      1994     5850
      1995     6200
      1996     6550
      1997     6859
      1998     7360
      1999     7570
      2000     8020
      2001     8500
      2002     10360
      2003     10980
      2004     11640
      2005     13160
      2006     13950
      2007     14780

      NOTE: grap doesn't care whether you separate data columns with a space or a tab so long as you're consistent.

      Adding Shapes and Other Features

      grap does more than just draw lines. It can print a grid. It can draw a circle, ellipse, or arrow. In fact, grap can draw just about anything that pic can.

      grap has a macro facility just like that of pic:

      define name X commands X

      For the delimiter, you can use any character that isn't in the command text. You can also use braces. grap permits up to nine arguments, just as pic does.

      In addition to data explicitly specified in a file, grap works with functions that more or less describe the data. The following code, for example, produces a sine curve:

      frame ht 1 wid 3
      draw solid
      for i from 0 to 2*pi by .1 do { next at i, sin(i) }

      Summary of grap Commands

      Table 26.1 summarizes the grap commands. Square brackets indicate that an argument is optional. A pipe between arguments means that you must use only one of the arguments.

        Table 26.1. Summary of grap commands.


      frame [ht expr] [wid expr] [[side] [descr]]

      Specifies the dimensions for the frame drawn around the graph



      Refers to the frame



      Describes the lines used to draw the frame. You can control dotting and dashing by specifying the distance between dots or the length of and distance between dashes.


      side list

      Specifies the placement of and the text for labels


      left|right|up|down expr

      Specifies the shift


      rjust|ljust, above|below, size expr

      Encloses items in quotation marks. You can modify the placement. size expr reduces the point size. This is useful for labels or for putting words or symbols in the graph itself.


      coord [name] [x expr,expr] [y expr,expr] [log x|log y|log log]

      Specifies points on a graph and suppresses padding


      ticks [side] in|out

      Specifies ticks on the side(s) of graph. The ticks can be inside or outside the frame.


      grid side [descr]

      Draws a grid with solid, dotted, dashed lines


      [name] expr, expr

      Identify a point in a graph


      line|arrow from point to point [descr]

      Draws a line (solid, dashed, dotted, and so on)


      circle at point [radius expr]

      Draws a circle


      draw [name] descr

      Draws a graph (solid, dotted, dashed, and so on)


      new [name]

      Draws a new graph in the same frame


      next name at point

      Continues plot of data in name at point. Default is current position.


      for var from expr to expr [by expr]

      Looping function for grap


      if expr then X anything X else X anything X

      Conditional statement for grap


      graph Picname

      Labels a graph. The label must start with an uppercase letter.


      define name X commands X

      Defines a macro


      copy "filename"

      Copies the specified file into the graph file. copy is used for data files.


      sh X anything X

      Executes a shell command from within grap


      pic anything

      Draws a pic construct from within grap


      var = expr

      Assigns a value to a variable

      In addition to the commands listed in Table 26.1, grap provides for predefined strings and built-in functions.

      Predefined strings include bullet, plus, box, star, dot, times, htick, vtick, square, and delta.

      Built-in functions include log (base 10), exp (base 10), int, sin, cos, atan2, sqrt, min, max, and rand.


      grap gives you a quick and relatively easy way of inserting graphs into memos or other text files. It can produce line and bar graphs, but no pie charts, no color, and no shading. Nevertheless, grap can be a useful tool. Like pic, grap is system-sensitive, so allow time for debugging.

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