Adding colour to polylines in Leaflet

@Kent Johnson <kent3737 at gmail.com> guess I jumped the gun!

Your code worked like a charm as long as the colours were all in order,
ie, none of them are repeating.
Like I mentioned, I am working with shipping data and the Color variable
is dependent on the ship?s speed. The code that you provided joins all the
line segments which have the same color.
So if red represents a speed less than 3 knots, then it will join all the
points irrespective of the timeline wherever the color is red.

What I am looking for is one continuous path where the same color might
repeat. Here?s a reproducible example:

library(leaflet)
x <- structure(list(lat = c(51.88783, 51.8878441, 51.887825, 51.88659,  51.8866959, 51.8874931, 51.89359, 51.8941269, 51.8977051, 51.8994331,  51.90773, 51.91324, 51.91604, 51.9216652, 51.93353, 51.9419365 ),
                     lon = c(4.28763342, 4.287635, 4.28765154, 4.29007339, 4.29562664,  4.29917, 4.30641174, 4.30561829, 4.29263353, 4.284498, 4.261132,  4.24711847, 4.241075, 4.23262, 4.21523666, 4.1927),
                     rateOfTurn = c(0L,  0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L),
                     sogKts = c(0, 0, 0, 2.1, 3.4, 4.6, 3.5, 3.8, 7.4, 7.9, 8.8,9.1, 9.2, 9.2, 0.3, 0.4),
                     cog = c(15, 15, 15, 122.2, 70.4,      70, 323.2, 315.3, 289.3, 290.9, 303.8, 303.7, 308.9, 324.5, 304.9, 301.4),
                     heading = c(163, 162, 163, 106, 71, 71, 303,      298, 289, 294, 303, 303, 310, 324, 304, 302),
                     timestamp = c("2018-07-19T05:27:34","2018-07-19T05:39:35", "2018-07-19T05:45:34", "2018-07-19T05:57:37",
                                   "2018-07-19T06:02:48", "2018-07-19T06:04:49", "2018-07-19T06:12:51", "2018-07-19T06:13:32",
                                   "2018-07-19T06:19:08", "2018-07-19T06:21:41",      "2018-07-19T06:28:42", "2018-07-19T06:32:50",
                                   "2018-07-19T06:34:37",      "2018-07-19T06:37:41", "2018-07-19T06:43:49", "2018-07-19T06:50:09"),
                     Color = c("red", "red", "red", "red", "orange", "orange","orange", "orange", "orange", "orange", "yellow", "yellow",
                               "yellow", "yellow", "red", "red")), row.names = 32:47, class = "data.frame")

#Kent's code

x$lastColor = dplyr::lag(x$Color)
map <-  leaflet(x)
map <- addTiles(map)
for( Color in
     levels(as.factor(x$Color))){
  map <- addPolylines(map,lng=~lon,lat=~lat,data=x[x$Color==Color | x$lastColor==Color,], color=~Color) }
map

As you can see, the last two observations are again in red color. But when
the map renders, it joins the last two observations with the first three.

I am not sure what to do here? Inserting a row of NAs would help? But I am
also using another javascript plugin (polylineDecorator) for adding
arrows to the direction of travel and that is intolerant to NAs.
Appreciate some help here.


Regards
Dhiraj Khanna
Mob:09873263331

On Sat, Sep 1, 2018 at 8:06 PM Dhiraj Khanna <dhirajkhanna at gmail.com>
wrote:

Thank you Kent, that worked like a charm!
Regards

Dhiraj Khanna
Mob:09873263331


On Sat, Sep 1, 2018 at 7:59 PM Kent Johnson <kent3737 at gmail.com> wrote:

You have to include the points where the colors change in both
polylines. Here is one way:

x$lastColor = dplyr::lag(x$Color)
map <-  leaflet(x)
map <- addTiles(map)
for( Color in
levels(as.factor(x$Color))){
  map <- addPolylines(map,lng=~lon,lat=~lat,data=x[x$Color==Color |
x$lastColor==Color,], color=~Color) }
map

Kent

On Sat, Sep 1, 2018 at 8:56 AM, Dhiraj Khanna <dhirajkhanna at gmail.com>
wrote:

@Kent they are appearing as three separate lines. I am hoping to see
them joint with no gaps. The transition from row 4 to row 5 is where the
speed has changed from 2.1 knots to 3.4 knots. I am hoping to see another
line from row 4 to row 5 in red colour. Similarly for the other disjoint
points.
Regards

Dhiraj Khanna
Mob:09873263331


On Sat, Sep 1, 2018 at 6:17 PM Kent Johnson <kent3737 at gmail.com> wrote:

Message: 5

Date: Sat, 1 Sep 2018 08:28:24 +0530
From: Dhiraj Khanna <dhirajkhanna at gmail.com>
To: r-sig-geo at r-project.org
Subject: [R-sig-Geo] Adding colour to polylines in Leaflet
Message-ID:
        <
CANHhK329-Y7hPJD9gSOs24mSqGkrjC481oQspNAgVisAw2JBoQ at mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

I am working with shipping data where I get the dynamic parameters of
a
ship like its position, speed, heading and rate of turn. I am then
trying
to plot this on a leaflet map and trying to colour the polylines
based on
the speed, but it always shows up in the same colour. Here?s some
sample
data:

<snip>
This is the code I have tried which doesn?t work:-

map <-  leaflet(x) map <- addTiles(map) for( Color in
levels(as.factor(x$Color))){   map <- addPolylines(map,
lng=~lon,lat=~lat,data=x[x$Color==Color,], color=~Color) } map

Regards
Dhiraj Khanna
Mob:09873263331

What are you expecting to see? When I run your code I get a map with
three lines, one red, one orange and one yellow.

Kent