R legend placement in a plot

Question

I have a plot that has data that runs into the area I d like to use for a legend   Is there a way to have the plot automatically put in something like a header space above the highest data points to fit the legend into   I can get it to work if I manually enter the ylim   arguments to expand the size and then give the exact coordinates of where I want the legend located  but I d prefer to have a more flexible means of doing this as it s a front end for a data base query and the data levels could have very different levels

User · Answer

You have to add the size of the legend box to the ylim range

#Plot an empty graph and legend to get the size of the legend
x <-1:10
y <-11:20
plot(x,y,type="n", xaxt="n", yaxt="n")
my.legend.size <-legend("topright",c("Series1","Series2","Series3"),plot = FALSE)

#custom ylim. Add the height of legend to upper bound of the range
my.range <- range(y)
my.range[2] <- 1.04*(my.range[2]+my.legend.size$rect$h)

#draw the plot with custom ylim
plot(x,y,ylim=my.range, type="l")
my.legend.size <-legend("topright",c("Series1","Series2","Series3"))

enter image description here

User · Answer

Edit 2017   use ggplot and theme legend position          library ggplot2  library reshape2   set seed 121  a sample 1 100 5  b sample 1 100 5  c sample 1 100 5   df   data frame number   1 5 a b c  df long  lt - melt df id vars    number   ggplot data df long aes x   number y value  colour variable    geom line     theme legend position  bottom     Original answer 2012  Put the legend on the bottom   set seed 121  a sample 1 100 5  b sample 1 100 5  c sample 1 100 5   dev off    layout rbind 1 2   heights c 7 1      put legend on bottom 1 8th of the chart  plot a type  l  ylim c min c a b c   max c a b c     lines b lty 2  lines c lty 3 col  blue      setup for no margins on the legend par mar c 0  0  0  0     c bottom  left  top  right  plot new   legend  center   groups  c  A   B   C    lty   c 1 2 3          col c  black   black   blue   ncol 3 bty   n

User · Answer

Building on  P-Lapointe solution  but making it extremely easy  you could use the maximum values from your data using max   and then you re-use those maximum values to set the legend xy coordinates  To make sure you don t get beyond the borders  you set up ylim slightly over the maximum values   a c rnorm 1000   b c rnorm 1000   par mfrow c 1 2   plot a ylim c 0 max a  1   legend x max a  0 5 legend  a  pch 1  plot a b ylim c 0 max b  1  pch 2  legend x max b -1 5 y max b  1 legend  b  pch 2

User · Answer

legend   will tell you   Arguments  x  y the x and y co-ordinates to be used to position the legend  They can be specified by keyword or in any way which is accepted by xy coords  See    Details       Details    Arguments x  y  legend are interpreted in a non-standard way to allow the coordinates to be specified via one or two arguments  If legend is missing and y is not numeric  it is assumed that the second argument is intended to be legend and that the first argument specifies the coordinates   The coordinates can be specified in any way which is accepted by xy coords  If this gives the coordinates of one point  it is used as the top-left coordinate of the rectangle containing the legend  If it gives the coordinates of two points  these specify opposite corners of the rectangle  either pair of corners  in any order    The location may also be specified by setting x to a single keyword from the list bottomright  bottom  bottomleft  left  topleft  top  topright  right and center  This places the legend on the inside of the plot frame at the given location  Partial argument matching is used  The optional inset argument specifies how far the legend is inset from the plot margins  If a single value is given  it is used for both margins  if two values are given  the first is used for x- distance  the second for y-distance

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