R：ifelse语句和seq（）函数参数

Question

I am trying to define some options for the sequences of my y-axis in a baseR plot loop. I am trying to achieve this by using an if else statement where I define the axis labels like this

if(any(y < 100000 & y > -100000)){plotlabels <- c(-20000000, 20000000, 10000)} else {plotlabels <- c(-20000000, 20000000, 1000)}

then comes the plot loop and after that I am calling an axis() command for the y axis like this

axis(2, at = seq(plotlabels), cex.axis=1, labels=TRUE, tcl=-0.3)

But this will not work correctly as I get a vector by using c() for plotlabels and if I print the result I get the following

seq(plotlabels)
[1] 1 2 3

How could I change the if else statement so that I get the correct sequence parameters according to the if else statement (-20000000, 20000000, 10000 or -20000000, 20000000, 1000)?

Answer 1

If you use seq with a vector with at least two elements, the function will return the numbers from one to the vector length.

vec <- c(-10, 10, 2)
seq(vec)
# [1] 1 2 3

You can use one of the following approaches to obtain a correct sequence:

seq(vec[1], vec[2], vec[3])
# [1] -10  -8  -6  -4  -2   0   2   4   6   8  10

do.call(seq, as.list(vec))
# [1] -10  -8  -6  -4  -2   0   2   4   6   8  10