map 上的绘图点，但仅限于特定年份

Question

I am doing GIS stuff in R and only want to plot points from certain years. Would I need to superset years, if so can I superset a range of years? I'm not totally sure how to make a reproducible example of this that wouldn't take a ton of time - it seems different than regular plotting.

Essentially, how do I only get certain points on the data frame to come up on the map? Subsetting years?

I have points set up as follows

points(x$longitude,y$latitude)

which plots all points, just want a range of years at a time. Thanks.

Answer 1

When you use the $ operator you are extracting a column of your data.frame x as a vector. A vector can be subset by a logical vector passed to square braces, returning the ith elements where the logical value is TRUE , eg c(TRUE, FALSE, TRUE) passed to c("a", "b", "c") as c("a", "b", "c")[c(TRUE, FALSE, TRUE)] would return a and c .

Logical vectors can be created automatically with logical operations. The key operators are

• == is equal to
• != is not equal to
• > greater than
• < less than
• >= greater than or equal to
• <= less than it equal to

And operations can be combined with & (and) and |(or), and logic can be reversed using ! (eg !3<4 would ask is three not less than four?).

As an example, c(1,2,3,4) >= 3 would produce FALSE FALSE TRUE TRUE .

Assuming you have a variable called year in x , you solution would look something like:

points(x$longitude[x$year>2005 & x$year<=2010], 
       y$latitude[ x$year>2005 & x$year<=2010)