[R-sig-Geo] Adding colour to polylines in Leaflet

[Dhiraj Khanna]

@Kent Johnson <kent3737 using 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 using 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 using 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$lastColor==Color,], color=~Color) }
>> map
>>
>> Kent
>>
>> On Sat, Sep 1, 2018 at 8:56 AM, Dhiraj Khanna <dhirajkhanna using gmail.com>
>> wrote:
>>
>>> @Kent they are appearing as three separate lines. I am hoping to see
>>> them joint with no gaps. The transition from row 4 to row 5 is where the
>>> speed has changed from 2.1 knots to 3.4 knots. I am hoping to see another
>>> line from row 4 to row 5 in red colour. Similarly for the other disjoint
>>> points.
>>> Regards
>>>
>>> Dhiraj Khanna
>>> Mob:09873263331
>>>
>>>
>>> On Sat, Sep 1, 2018 at 6:17 PM Kent Johnson <kent3737 using gmail.com> wrote:
>>>
>>>> Message: 5
>>>>> Date: Sat, 1 Sep 2018 08:28:24 +0530
>>>>> From: Dhiraj Khanna <dhirajkhanna using gmail.com>
>>>>> To: r-sig-geo using r-project.org
>>>>> Subject: [R-sig-Geo] Adding colour to polylines in Leaflet
>>>>> Message-ID:
>>>>>         <
>>>>> CANHhK329-Y7hPJD9gSOs24mSqGkrjC481oQspNAgVisAw2JBoQ using mail.gmail.com>
>>>>> Content-Type: text/plain; charset="utf-8"
>>>>>
>>>>> I am working with shipping data where I get the dynamic parameters of a
>>>>> ship like its position, speed, heading and rate of turn. I am then
>>>>> trying
>>>>> to plot this on a leaflet map and trying to colour the polylines based
>>>>> on
>>>>> the speed, but it always shows up in the same colour. Here’s some
>>>>> sample
>>>>> data:
>>>>>
>>>>> <snip>
>>>>> This is the code I have tried which doesn’t work:-
>>>>>
>>>>> map <-  leaflet(x) map <- addTiles(map) for( Color in
>>>>> levels(as.factor(x$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
>>>>
>>>>
>>

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