[R] Color in stripchart

[Gerrit Eichner]

Dear Robin,

if you study stripchart's code (graphics:::stripchart) carefully
you will find out that the elements of the vector provided to the
col-argument (and the pch-argument as well) are selected by iterating
along the groups (in your case year). I don't seen easy solution for
your problem using stripchart, but you may want to look at the
examples of function beeswarm in package beeswarm.

  Hth  --  Gerrit

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Dr. Gerrit Eichner                   Mathematical Institute, Room 212
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Am 10.03.2021 um 14:08 schrieb Dr. Robin Haunschild:
> Dear fellow R users,
> 
> I'd like to color individual points in a stripchart. This works well as
> long as I have only a single value per y axis category:
> 
> df <- data.frame(year = seq(2011, 2018), value = seq(10,80, 10))
> df$color <- 'black'
> df[df$value<33,]$color <- 'blue'
> df[df$value>66,]$color <- 'red'
> stripchart(df$value ~ df$year, pch=18, col=df$color, method='stack')
> 
> When I use multiple values per y axis category, all points in a specific
> y axis category have the same color:
> 
> set.seed(20210310)
> years <- sample(x=seq(2011, 2018), size = 365*8, replace = TRUE)
> values <- sample(x=seq(0,100), size = 365*8, replace = TRUE)
> df <- data.frame(year = years, value = values)
> df$color <- 'black'
> df[df$value<33,]$color <- 'blue'
> df[df$value>66,]$color <- 'red'
> stripchart(df$value ~ df$year, pch=18, col=df$color, method='stack')
> 
> I'd expect to see all points with a value below 33 in blue color, all
> points with a value above 66 in red color, and the remaining points in
> black color.
> 
> I can use a black stripchart plot as basis and plot blue and red points
> over the black ones, but I do not get the stacking right:
> 
> stripchart(df$value ~ df$year, pch=18, method='stack')
> points(df[df$color=='blue',]$value, df[df$color=='blue',]$year-2010,
> type='p', pch=18, col='blue')
> points(df[df$color=='red',]$value, df[df$color=='red',]$year-2010,
> type='p', pch=18, col='red')
> 
> Am I somehow misusing the stripchart function?
> 
> 
> Best regards,
> 
> Robin
> 
> 
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