CODEWITHSUNDEEP
rplot
Joe
Joe

Reputation: 1768

Why is the last x-axis label omitted?

In the following example, the last x-axis label ("4.0") is omitted.

df <- data.frame(x = c(1, 2, 3.8), y = c(1, 2, 3))
#png(filename = "cutoff.png")
plot(df$x, df$y, xaxt = "n")
axis(side = 1, at = seq(0, 4, 0.5), labels = seq(0, 4, 0.5))
#dev.off()

How to prevent this behaviour? enter image description here

Upvotes: 1

Views: 54

Answers (2)

G5W
G5W

Reputation: 37661

As @griffinevo answered (+1), If you want the axis limits to go to 4, you must specify that using xlim. However, it is probably worth explaining how the default limits are computed. This is explained in the documentation, but in a slightly obscure place. On the help page ?par search for xaxs. There you will see

Style "r" (regular) first extends the data range by 4 percent at each end and then finds an axis with pretty labels that fits within the extended range.

In your case, the data ranges from 1 to 3.8. So plot will look for pretty labels inside the range 

1 - 0.04*(3.8-1) = 0.888   
    to 
3.8 + 0.04*(3.8-1) = 3.912

4 is outside of this range and so will not appear as an axis label. For completeness, it is worth noting that "pretty" sounds like just a word, but actually has a technical meaning here - related to the pretty function. If you look at the help page ?pretty You will see the description:

Compute a sequence of about n+1 equally spaced ‘round’ values which cover the range of the values in x. The values are chosen so that they are 1, 2 or 5 times a power of 10.

There is additional detail on the help page.

Upvotes: 2

rg255
rg255

Reputation: 4169

You axis limit does not include 4; you need to overwrite the default limits of the plot (which it derives from the data) using xlim:

plot(df$x, df$y, xaxt = "n", xlim = c(1, 4))

enter image description here

Note that when using axis your specification of at will become your labels unless you overwrite that, so your script doesn't need to specify labels; your script can become:

axis(side = 1, at = seq(0, 4, 0.5))

Upvotes: 2

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