title: How to use different symbols in dotplot based on vector values
body: <p>I have location (coordinates) and environmental data and I would like to create dot plots for each of the environmental variables in the dataset (see sample data and code below). Instead of a single symbol for all of the points in each dot plot (e.g. pch=16), I would like to use a unique symbol determined by the one-degree line of latitude, e.g. abs(latitude).</p>
  
  <p>My R sample dataset:</p>
  
  <pre><code>WW_Covs &lt;- structure(list(Latitude = c(62.4419, 67.833333, 65.95, 63.72935,
  60.966667, 60.266667, 55.660455, 62.216667, 61.3, 61.4, 62.084139, 55.662566, 
  64.48508, 63.208354, 62.87591, 62.70856, 62.64009, 63.79488, 59.55, 62.84206), BIO_02 
  = c(87, 82, 75, 70, 77, 70, 59, 84, 84, 79, 85, 60, 91, 87, 74, 74, 76, 70, 76, 74), 
  BIO_03 = c(26, 23, 25, 26, 25, 24, 25, 25, 26, 25, 26, 26, 24, 25, 24, 25, 25, 25, 26, 
  24), BIO_04 = c(8443, 9219, 7594, 6939, 7928, 7593, 6160, 8317, 8167, 7972, 8323, 
  6170, 9489, 8578, 7814, 7680, 7904, 7149, 7445, 7803), BIO_05 = c(201, 169, 151, 166, 
  194, 210, 202, 205, 204, 186, 205, 200, 200, 195, 170, 154, 180, 166, 219, 170), 
  BIO_06 = c(-131, -183, -144, -102, -107, -75, -26, -119, -113, -120, -120, -28, -169, 
  -143, -131, -142, -124, -111, -72, -129), BIO_08 = c(128, 109, 85, 78, 122, 145, 153, 
  134, 130, 126, 132, 152, 120, 119, 115, 98, 124, 104, 147, 115), BIO_09 = c(-31, -81, 
  -16, 13, -60, -6, 25, -25, -25, -70, -25, 23, -56, -39, -47, -60, -39, 8, 0, -46),
  BIO_12 = c(667, 481, 760, 970, 645, 557, 645, 666, 652, 674, 670, 670, 568, 598, 650, 
  734, 620, 868, 571, 658), BIO_13 = c(78, 77, 96, 109, 85, 70, 67, 77, 84, 93, 78, 68, 
  72, 78, 93, 99, 90, 96, 72, 93), BIO_15 = c(23, 40, 25, 21, 36, 30, 21, 24, 28, 34, 
  24, 22, 28, 29, 34, 32, 36, 22, 30, 34), BIO_19 = c(147, 85, 180, 236, 108, 119, 154, 
  149, 135, 118, 148, 162, 117, 119, 120, 141, 111, 204, 111, 122)), .Names = 
  c("Latitude", "BIO_02", "BIO_03", "BIO_04", "BIO_05", "BIO_06", "BIO_08", "BIO_09", 
  "BIO_12", "BIO_13", "BIO_15", "BIO_19"), row.names = c(1:20), class = "data.frame")
  </code></pre>
  
  <p>My R dotplot code:</p>
  
  <pre><code>library(lattice)    
  dotplot(as.matrix(WW_Covs[,-c(1:8)]), groups = FALSE,
              strip = strip.custom(bg = 'white', par.strip.text = list(cex = 0.8)), 
              scales = list(x = list(relation = "free"), y = list(relation = "free"), 
              draw = FALSE), col = 1, cex  = 0.5, pch = 16, xlab = "Value of the variable",
              ylab = "Order of the data from text file")
  </code></pre>