Shapes and line types

Problem

You want to use different shapes and line types in your graph.

Solution

plot of chunk unnamed-chunk-2

plot of chunk line_types

Note that with bitmap output, the filled symbols 15-18 may render without proper anti-aliasing; they can appear jagged, pixelated, and not properly centered, though this varies among platforms. Symbols 19 and 21-25 have an outline around the filled area, and will render with smoothed edges on most platforms. For symbols 21-25 to appear solid, you will also need to specify a fill (bg) color that is the same as the outline color (col); otherwise they will be hollow.

Standard graphics

Use the pch option to set the shape, and use lty and lwd to set the line type and width. The line type can be specified by name or by number.

  1. set.seed(331)
  3. # Plot some points with lines
  4. # Set up the plotting area
  5. par(mar=c(3,3,2,2))
  6. plot(NA, xlim=c(1,4), ylim=c(0,1))
  8. # Plot solid circles with solid lines
  9. points(1:4, runif(4), type="b", pch=19)
  10. # Add open squares with dashed line, with heavier line width
  11. points(1:4, runif(4), type="b", pch=0,  lty=2, lwd=3)
  13. points(1:4, runif(4), type="b", pch=23,   # Diamond shape
  14.        lty="dotted", cex=2,               # Dotted line, double-size shapes
  15.        col="#000099", bg="#FF6666")       # blue line, red fill

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ggplot2

With ggplot2, shapes and line types can be assigned overall (e.g., if you want all points to be squares, or all lines to be dashed), or they can be conditioned on a variable.

  1. # Sample data
  2. df <- read.table(header=T, text='
  3.   cond xval yval
  4.      A    1  2.0
  5.      A    2  2.5
  6.      B    1  3.0
  7.      B    2  2.0
  8. ')
  11. library(ggplot2)
  13. # Plot with standard lines and points
  14. # group = cond tells it which points to connect with lines
  15. ggplot(df, aes(x=xval, y=yval, group = cond)) +
  16.     geom_line() +
  17.     geom_point()
  19. # Set overall shapes and line type
  20. ggplot(df, aes(x=xval, y=yval, group = cond)) +
  21.     geom_line(linetype="dashed",  # Dashed line
  22.               size = 1.5) +       # Thicker line
  23.     geom_point(shape = 0,         # Hollow squares
  24.                size = 4)          # Large points
  26. # Condition shapes and line type on variable cond
  27. ggplot(df, aes(x=xval, y=yval, group = cond)) +
  28.     geom_line(aes(linetype=cond), # Line type depends on cond
  29.               size = 1.5) +       # Thicker line
  30.     geom_point(aes(shape=cond),   # Shape depends on cond
  31.                size = 4)          # Large points
  34. # Same as previous, but also change the specific linetypes and
  35. # shapes that are used
  36. ggplot(df, aes(x=xval, y=yval, group = cond)) +
  37.     geom_line(aes(linetype=cond), # Line type depends on cond
  38.               size = 1.5) +       # Thicker line
  39.     geom_point(aes(shape=cond),   # Shape depends on cond
  40.                size = 4) +        # Large points
  41.     scale_shape_manual(values=c(6,5)) +                  # Change shapes
  42.     scale_linetype_manual(values=c("dotdash", "dotted")) # Change linetypes

plot of chunk unnamed-chunk-4plot of chunk unnamed-chunk-4plot of chunk unnamed-chunk-4plot of chunk unnamed-chunk-4

By default, ggplot2 uses solid shapes. If you want to use hollow shapes, without manually declaring each shape, you can use scale_shape(solid=FALSE). Note, however, that the lines will visible inside the shape. To avoid this, you can use shapes 21-25 and specify a white fill.

  1. # Hollow shapes
  2. ggplot(df, aes(x=xval, y=yval, group = cond)) +
  3.     geom_line(aes(linetype=cond), # Line type depends on cond
  4.               size = 1.5) +       # Thicker line
  5.     geom_point(aes(shape=cond),   # Shape depends on cond
  6.                size = 4)  +       # Large points
  7.     scale_shape(solid=FALSE)
  9. # Shapes with white fill
  10. ggplot(df, aes(x=xval, y=yval, group = cond)) +
  11.     geom_line(aes(linetype=cond), # Line type depends on cond
  12.               size = 1.5) +       # Thicker line
  13.     geom_point(aes(shape=cond),   # Shape depends on cond
  14.                fill = "white",    # White fill
  15.                size = 4)  +       # Large points
  16.     scale_shape_manual(values=c(21,24))  # Shapes: Filled circle, triangle

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Note

This code will generate the chart of line types seen at the top.

  1. par(mar=c(0,0,0,0))
  3. # Set up the plotting area
  4. plot(NA, xlim=c(0,1), ylim=c(6.5, -0.5),
  5.     xaxt="n", yaxt="n",
  6.     xlab=NA, ylab=NA )
  8. # Draw the lines
  9. for (i in 0:6) {
  10.     points(c(0.25,1), c(i,i), lty=i, lwd=2, type="l")
  11. }
  12. # Add labels
  13. text(0, 0, "0. 'blank'"   ,  adj=c(0,.5))
  14. text(0, 1, "1. 'solid'"   ,  adj=c(0,.5))
  15. text(0, 2, "2. 'dashed'"  ,  adj=c(0,.5))
  16. text(0, 3, "3. 'dotted'"  ,  adj=c(0,.5))
  17. text(0, 4, "4. 'dotdash'" ,  adj=c(0,.5))
  18. text(0, 5, "5. 'longdash'",  adj=c(0,.5))
  19. text(0, 6, "6. 'twodash'" ,  adj=c(0,.5))