R help - Nov 2007 - problem with plotting table

Hi all,

Let us have:

x<-1:10
y<-x/2
plot(table(x), type="p")
points(table(y), pch=2)


Why does the last command plots the values of table(y) using the x  
coordinates of table(x)???
Am I doing something wrong?
What would be a way of plotting the points of table(y) on their place?

#this problem also occurs with:
plot(table(y), type="p")
points(table(x), pch=2)


Thank you very much,
Carlos

Carlos Gershenson wrote:
> Hi all,
>
> Let us have:
>
> x<-1:10
> y<-x/2
> plot(table(x), type="p")
> points(table(y), pch=2)
>
>
> Why does the last command plots the values of table(y) using the x  
> coordinates of table(x)???
>   
It's just a coincidence.  It's actually using the indices 1:10, 
regardless of the values of x.

You've given points() a vector of 10 values to plot, and by default it 
plots them against their index.

To get what you want you need

temp <- table(y)
points(names(temp), temp)

The reason plot() worked is because it has a method for tables, but 
points() does not.  In general the high level plot functions in R tend 
to have lots of methods, but the low level ones make you do the work.

Duncan Murdoch
> Am I doing something wrong?
> What would be a way of plotting the points of table(y) on their place?
>
> #this problem also occurs with:
> plot(table(y), type="p")
> points(table(x), pch=2)
>
>
> Thank you very much,
> Carlos
>
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>

On Tue, 2007-11-27 at 13:01 -0500, Carlos Gershenson
wrote:
> Hi all,
> 
> Let us have:
> 
> x<-1:10
> y<-x/2
> plot(table(x), type="p")
> points(table(y), pch=2)
> 
> 
> Why does the last command plots the values of table(y) using the x  
> coordinates of table(x)???
> Am I doing something wrong?
> What would be a way of plotting the points of table(y) on their place?
> 
> #this problem also occurs with:
> plot(table(y), type="p")
> points(table(x), pch=2)
> 
> 
> Thank you very much,
> Carlos

Hi Carlos 

In your command plot(table(y), type="p"), you plot a numeric part of
table(y), in this case:

y
0.5   1 1.5   2 2.5   3 3.5   4 4.5   5 
  1   1   1   1   1   1   1   1   1   1

So you plot the number 1 always. Same for table (x).

Have two possible solutions:

plot(as.numeric(names(table(x))), type="p")
points(as.numeric(names(table(y))), pch=2)


OR

x<-1:10
y<-x/2
plot(x, type="p")
points(y, pch=2)

If you need more help send a mail



-- 
Bernardo Rangel Tura, M.D,MPH,Ph.D
National Institute of Cardiology
Brazil

Thank you very much Duncan, that did the works.

Thank you also Gavin and Bernardo for your feedback.

Best regards,
Carlos