[R] plot factors with dots in R

[PIKAL Petr]

Hi.
It is probably somewhere in docs, but factors are actually numerics vith
labels. 

So with your original data frame

df$x <- factor(df$x)
plot(as.numeric(df$x), df$y)

gives you points. You need to set labels to x axis though.

Cheers
Petr

> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Luigi Marongiu
> Sent: Thursday, August 27, 2020 2:16 PM
> To: r-help <r-help using r-project.org>
> Subject: [R] plot factors with dots in R
> 
> Hello,
> I have a dataframe as follows:
> ```
> x = c("0 pmol", "10 pmol", "100 pmol", "1000 pmol")
> y = c(0.9306, 1.8906, 2.2396, 2.7917)
> df = data.frame(x, y)
> 
> > str(df)
> 'data.frame': 4 obs. of  2 variables:
>  $ x: chr  "0 pmol" "10 pmol" "100 pmol" "1000 pmol"
>  $ y: num  0.931 1.891 2.24 2.792
> ```
> I would like to visualize the data with the classic dots (pch=16) but:
> ```
> > plot(df$y ~ df$x)
> Error in plot.window(...) : need finite 'xlim' values
> In addition: Warning messages:
> 1: In xy.coords(x, y, xlabel, ylabel, log) : NAs introduced by coercion
> 2: In min(x) : no non-missing arguments to min; returning Inf
> 3: In max(x) : no non-missing arguments to max; returning -Inf
> ```
> which is right because x is not numeric, so I took the factor:
> ```
> plot(df$y ~ factor(df$x)) # gives bars instead of dots
> plot(df$y ~ factor(df$x), pch = 16) # this also
> ```
> I tried to convert directly the dataframe:
> ```
> df$x = lapply(df$x, factor)
> > str(df)
> 'data.frame': 4 obs. of  2 variables:
>  $ x:List of 4
>   ..$ : Factor w/ 1 level "0 pmol": 1
>   ..$ : Factor w/ 1 level "10 pmol": 1
>   ..$ : Factor w/ 1 level "100 pmol": 1
>   ..$ : Factor w/ 1 level "1000 pmol": 1
>  $ y: num  0.931 1.891 2.24 2.792
> 
> > plot(r$y ~ r$x, pch = 16)
> Error in plot.window(...) : need finite 'xlim' values
> In addition: Warning messages:
> 1: In xy.coords(x, y, xlabel, ylabel, log) : NAs introduced by coercion
> 2: In min(x) : no non-missing arguments to min; returning Inf
> 3: In max(x) : no non-missing arguments to max; returning -Inf
> ```
> If I try to pass the number of levels:
> ```
> plot(df$y ~ factor(df$x, 1:4), pch = 16) # this draw a boxplot with
> all data on level 1
> 
> > df$x = lapply(df$x, factor(1:4))
> Error in match.fun(FUN) :
>   'factor(1:4)' is not a function, character or symbol
> ```
> 
> Since the transformation has given only one level (1), my questions are:
> How do I tell R to use a dot instead of a line?
> What is the correct way of setting factors?
> 
> 
> --
> Best regards,
> Luigi
> 
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