[R] Join points with arrows based a TIME variable

[Uwe Ligges]

zhijie zhang wrote:
> Hi Uwe,
>   It works. Why does the following argument generate different results?
> with(data, arrows(x[-length(x)], y[-length(x)], x[-1], y[-1]))
> #correct,multiple joins

In the former you select all elements of the vectors except the first or 
last one, respectively.

In the next call you select just one arguemnt of each vector, namely the 
first or last one.

Uwe Ligges


> with(data, arrows(x[1], y[1], x[length(x)], y[length(x)]))  #wrong,seems to
> be only one join
>   From the ?arrows, the second argument should work. What is the problem?
>   Thanks a lot.
> #codes:
> x<-c(1:6);y<-c(1:6);time<-c(6:1);data<-cbind(x,y,time);data
> data<-data.frame(data[order(data[,"time"]),])
> with(data, plot(x,y))
> with(data, arrows(x[-length(x)], y[-length(x)], x[-1], y[-1]))
> 
> with(data, plot(x,y))
> with(data, arrows(x[1], y[1], x[length(x)], y[length(x)]))
> 2009/11/4 Uwe Ligges <ligges at statistik.tu-dortmund.de>
> 
>>
>> zhijie zhang wrote:
>>
>>> Hi,
>>>  I have a data set with three variables,X Y and Time. X and Y are the
>>> coordinates of points, i want to join these points according to the Time
>>> sequence using arrows?
>>> Demo Example data:
>>>
>>>> x<-c(1:6)
>>>> y<-c(1:6)
>>>> time<-c(6:1)
>>>> data<-cbind(x,y,time)
>>>> data
>>>>
>>>     x y time
>>> [1,] 1 1    6
>>> [2,] 2 2    5
>>> [3,] 3 3    4
>>> [4,] 4 4    3
>>> [5,] 5 5    2
>>> [6,] 6 6    1
>>>  I hope to join the six points with points' time=1 as starting point and
>>> points' time=6 as endpoint. So the sequence is time=1,2,3,4,5,6 and join
>>> the
>>> corresponding points with arrows.
>>>  Any ideas on it?
>>>
>>
>> data <- data.frame(data[order(data[,"time"]),])
>> with(data, plot(y ~ x))
>> with(data, arrows(x[-length(x)], y[-length(x)], x[-1], y[-1]))
>>
>>
>> Uwe Ligges
>>
>>
>>        [[alternative HTML version deleted]]
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