Gantt style time line plot (in base R)

Question

I have a dataframe that looks like this:

       person n start end
1         sam 6     0   6
2        greg 5     6  11
3     teacher 4    11  15
4         sa         


        

Answer 1

Pretty similar to @John's approach, but since I did it, I will post it :)

Here's a generic function to plot a gantt (no dependencies):

plotGantt <- function(data, res.col='resources', 
                      start.col='start', end.col='end', res.colors=rainbow(30))
{
  #slightly enlarge Y axis margin to make space for labels
  op <- par('mar')
  par(mar = op + c(0,1.2,0,0)) 

  minval <- min(data[,start.col],na.rm=T)
  maxval <- max(data[,end.col],na.rm=T)

  res.colors <- rev(res.colors)
  resources <- sort(unique(data[,res.col]),decreasing=T)

  plot(c(minval,maxval),
       c(0.5,length(resources)+0.5),
       type='n', xlab='Duration',ylab=NA,yaxt='n' )
  axis(side=2,at=1:length(resources),labels=resources,las=1)
  for(i in 1:length(resources))
  {
    yTop <- i+0.1
    yBottom <- i-0.1
    subset <- data[data[,res.col] == resources[i],]
    for(r in 1:nrow(subset))
    {
      color <- res.colors[((i-1)%%length(res.colors))+1]
      start <- subset[r,start.col]
      end <- subset[r,end.col]
      rect(start,yBottom,end,yTop,col=color)
    }
  }
  par(mar=op) # reset the plotting margins
}

Usage example:

data <- read.table(text=
'"person","n","start","end"
"sam",6,0,6
"greg",5,6,11
"teacher",4,11,15
"sam",4,15,19
"greg",5,19,24
"sally",5,24,29
"greg",4,29,33
"sam",3,33,36
"sally",5,36,41
"researcher",6,41,47
"greg",6,47,53',sep=',',header=T)

plotGantt(data, res.col='person',start.col='start',end.col='end',
          res.colors=c('green','blue','brown','red','yellow'))

Result:

Answer 2

While the y-axis is categorical all you need to do is assign numbers to the categories (1:5) and track them. Using the default as.numeric() of the factor will usually number them alphabetically but you should check anyway. Make your plot with the xaxt = 'n' argument. Then use the axis() command to put in a y-axis.

axis(2, 1:5, myLabels)

Keep in mind that whenever you're plotting the only way to place things is with a number. Categorical x or y values are always just the numbers 1:nCategories with category name labels in place of the numbers on the axis.

Something like the following gets you close enough (assuming your data.frame object is called datf)...

datf$pNum <- as.numeric(datf$person)
plot(datf$pNum, xlim = c(0, 53), type = 'n', yaxt = 'n', xlab ='Duration (words)', ylab = 'person', main = 'Speech Duration')
axis(2, 1:5, sort(unique(datf$person)), las = 2, cex.axis = 0.75)
with(datf, segments(start, pNum, end, pNum, lwd = 3, lend=2))

Answer 3

You say you want a base R solution, but you don't say why. Since this is one line of code in ggplot, I show this anyway.

library(ggplot2)
ggplot(dat, aes(colour=person)) + 
    geom_segment(aes(x=start, xend=end, y=person, yend=person), size=3) +
    xlab("Duration")