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An important aspect to developing data products is having a way
to create interactive maps.
Leaflet is a JavaScript library, and
then there is an associated Leaflet package for R that makes use of this
JavaScript library to create interactive maps within your R environment.
And it's especially convenient within RStudio because it brings it up in
the RStudio window.
So we're just going to go ahead and go through some Leaflet examples and
get you started with the bare minimum to get going on this, and
I think you'll get the extended rather quickly.
So, and I should say there's several other ways to create interactive maps.
GoogleVis is another one, and so I think Leaflet
is worth covering on its own just because it's so
widely accepted and widely used among the R crowd.
But again, I would also say, look up, in our googleVis lecture we also talk about
creating maps using googleVis, which directly access Google Maps.
And there's still some other ways, but
I think those two might be the two most popular.
So you want to make sure you install it first, I won't go through this,
just install.packages("leaflet").
Now let's just go through a code example where we create our
first Leaflet map in R.
So here I have the R mark down document for the next couple of slides.
I have the whole R mark down document, but here's the code for
the next couple of slide.
It has two separate sections, one that just displays it as code, and one that,
the separate one that evaluates it.
So you have to call library(leaflet).
And then, let me just run these three commands, and then we'll talk about them.
So, the first thing I want to comment on, so I ran the commands and
there you can see your map.
And then you can zoom in, of course, as much as you'd like.
So, it is a, and this is in the RStudio viewer pane.
So it's not a plot, it's in the kind of browser viewer that's in RStudio.
Okay, so, the first thing I'd like to mention is something that we're
going to use heavily in these set of lectures, which is the piping notation.
So, what this code basically is equivalent to is,
imagine if I wrote up my_map=leaflet(),
okay, and then my_map=addTiles(my_map), okay?
So let me get rid of my map over here and then run these three lines, okay?
And you'll see it does the same thing.
It generates the same map.
So this code right here, right, is identical to this code right here.
That's what the piping notation is doing.
It's taking this output, my_map, and
then piping it to this next command, adding it as the first argument and
then reassigning it to the variable here, okay?
So, and that's a lot cleaner code, and easier to read,
once you get to used to it than what I had written below.
Okay, so the first part leaflet just kind of generates the map.
And then the addTiles is adding the first set of content.
And we'll talk in a little bit about how to actually do some useful things,
like add markers and so on.
But just first try to do this, just generate a world map, zoom around,
make sure you can install a Leaflet library, and this is step one and
then now we'll go on to some more interesting things.
Brian Caffo, PhDProfessor, Biostatistics
Jeff Leek, PhDAssociate Professor, Biostatistics
Roger D. Peng, PhDAssociate Professor, Biostatistics
