R晶格X轴刻度线间距

Question

Plotting some values against date like

01/31/1996      -7.3667
02/29/1996       0.9413
03/31/1996       9.3252
04/30/1996       0.3147
05/31/1996       8.8593
06/30/1996      10.0297
07/31/1996       0.64i3
08/31/1996       2.1397
09/30/1996       0.6759
10/31/1996      -1.5579
11/30/1996       2.9493
....             ....
goes on till 2012 Nov

using barchart in R lattice, I got a reasonable looking graph but the labels on the x axis are all squished together and just looks like a huge glob of text. I think it's outputting every date from above in literal form and trying to fit it all into the space but what I'd really like is just 4 or 5 tickmarks increments of 4 years like

1996            20000            2004            2008            2012 

evenly spaced out

I'm not sure how these dates are being interpreted so using just tick.marks=5 or scales=list(x=list(at=seq(1996,2012,4) ) is not working. I also tried the following but the tick marks are uneven (sometimes in 4 years, sometimes 5) and do not really correspond to the exact positions of the actual data.

> df <- data.frame(x=paste0(rep(1996:2012, each=12), paste0("Q", 1:12)), y=1:204)
> x.tick.number <- 10
> x.tick.number <- 8
> at <- seq(1, nrow(df), length.out=x.tick.number)
> labels <- round(seq(1996, 2012, length.out=x.tick.number))
> barchart(V3~V1,  data = differences,col=c("green3"),origin=0,box.ratio=40, lty=0,reference=TRUE,stack=TRUE,main ="testing",ylab = list("values", cex=1.3), xlab = list
("dates",cex=1.3),par.settings=list (axis.text=list(cex=1.5), axis.line = list(lwd=3)),scales=list(y=list(tick.number=8, rot=90 ), x=list(at=at, labels=labels)))

Any other suggestions? Also I have date ranges from -25 to 20 on the y axis with tick marks at increments of 5 but I'd like 5 smaller tickmarks within each. How do I control this. Thanks.

Answer 1

I assume that you are plotting each month as a different bar and that every month is in hte data. If so, I think you can do this:

My_at<-c(6,54,102,150,198)

This puts the tick in June of 1996, 2000, 2004, 2008 and 2012

then in the barchart function:

scales=list(x=list(at=at,labels=c("1996","2000","2004","2008","2012")))

Without a reproducible example I can't test this - but this is the basic idea.

If you don't have data for every month you will need to change the values in at accordingly.

Edit in response to comments

The numbers in the labels arguement (eg "2000", "2004" etc) are just the text to use for the tick labels, and can be changed as desired. The values placed in 'My_at` are just the bar number - so the 6 means put the tick label below the 6th bar, and the 54 is the 54th bar and so on. You can put a label beyond where you have data (such as the 500th bar) if you wanted. To move the last tick to the left, just decrease the last number. I you make it 192 instead of 198 that will correspond to January 2012.

Finally to draw the ticks use:

scales=list(x=list(at=at,labels=c("1996","2000","2004","2008","2012"), draw=TRUE,
              tck=2 ))

The draw=TRUE indicates that labels and tick marks should be drawn, and tck=2 controls the length of the tick marks. You can try different values to find one you like.