[ncl-talk] Looking to create a scatterplot of x vs y colored based on value of z

[Mary Haley]

Hi Tyler,

You unfortunately can't use xyMarkerColor in this way, where you give it a
bunch of markers and then an array of colors to apply to each marker.  The
XY plotting in NCL wants to apply the same color to a set of markers.

One way you can do this is to create a blank plot with the correct axes
limits, and then use gsn_polymarker. I did this in a hurry because I have a
meeting to go to, but see the attached.

You may also want to visit this page for some more examples (search for
"marker"):

http://www.ncl.ucar.edu/Applications/polyg.shtml

--Mary


On Wed, Jun 6, 2018 at 4:11 PM, Tyler Herrington <therring at uwaterloo.ca>
wrote:

> Good Afternoon,
>
> I am looking to create a scatterplot of Change in Tree Fraction vs Change
> in Grass Fraction where the scatterplot values are colored based on their
> change in albedo value.
>
> Each of Tree, Grass and Albedo have been converted into 1D arrays with
> 6480 values
>
> Albedo values vary between -0.415 and +0.153, and I am looking to create a
> colormap with 19 colors from the GMT_polar colormap.
>
> My script works ok for cases where z = ind() returns a single value (which
> is the case when i = 0), however it fails if z returns 2 or more values
> (for example when i=1), and thus I was hoping to put this out to see if
> anyone had any suggestions on how to fix this problem?
>
> begin
>
> ;********************************************
> ; Read in Tundra and Boreal Albedo Feedbacks
> ;********************************************
>
> dirA = "/praid/users/herringtont/Caldwell_2016/GFDL_Albedo/albedo/"
> dirV = "/praid/users/herringtont/Caldwell_2016/Vegetation_Data/"
>
> A1 = dirA+"albedo_Amon_GFDL-ESM2G_rcp45_r1i1p1_208001-209912_
> avg_diff_LandOnly_NH.nc"
> T1 = dirV+"treeFrac_Lmon_GFDL-ESM2G_rcp45_r1i1p1_diff_Frac_LandOnly_NH.nc"
> G1 = dirV+"grassFrac_Lmon_GFDL-ESM2G_rcp45_r1i1p1_diff_Frac_
> LandOnly_NH.nc"
>
> A2 = addfile(A1,"r")
> T2 = addfile(T1,"r")
> G2 = addfile(G1,"r")
>
> ALB = A2 ->rsuscs(4,:,:)
> Grass = G2 ->grassFrac(4,:,:)
> Tree = T2 ->treeFrac(4,:,:)
>
> ;********************************************
> ; Reshape ALB, Tree, and Grass from 2D to 1D
> ;********************************************
>
> ALB1d = ndtooned(ALB)
> Tree1d = ndtooned(Tree)
> Grass1d = ndtooned(Grass)
>
> ;************************************
> ; Create Color Scale for Scatterplot
> ;************************************
>
> dALB = dimsizes(ALB1d)
> colorALB = new(dALB,"integer")
> clrs = (/2,3,4,5,6,7,8,9,10,12,13,14/)
>
> i = 0
> do while (i.le.10)
>
> j = i-1
>
> if (i.eq.0) then
>
>   VAL1 = -0.45
>   VAL2 = -0.40
>
> else
>   VAL1 = -0.35+(0.05*j)
>   VAL2 = -0.30+(0.05*j)
> end if
>
> print(VAL1)
> print(VAL2)
>
> z = ind(ALB1d.gt.VAL1.and.ALB1d.lt.VAL2)
>
> print(z)
> print(i)
>
> colorALB(z) = clrs(i)
>
> i = i+1
>
> end do
>
> print(colorALB)
> ;******************************************************
> ; Create April Mean Veg vs Alb Change Scatterplot
> ;******************************************************
>
> wks = gsn_open_wks("png","GFDL_Veg_Alb_Apr_Scatter_Color")
>
> gsn_define_colormap(wks,"GMT_polar")
>
> res = True
> res at gsnDraw            = False        ; Don't draw plot or advance
> res at gsnFrame           = False        ; frame. Will do this later.
>
> res at tiXAxisString = "Change in Tree Fraction"
> res at tiYAxisString = "Change in Grass Fraction"
>
>
> square = NhlNewMarker(wks, "y", 35, 0.0, 0.0, 1., 0.5, 0.)
>   res at xyMarkLineMode     = "Markers"
>   res at xyMarkerThicknessF = 2.5
>   res at xyMarkerColor     = colorALB
>   res at xyMarker           = square     ; this is a filled square
>
>
> plot = gsn_csm_xy(wks,Tree1d,Grass1d,res)
>
>   maximize_output(wks,False)
>
> system("mv *.png /home/herringtont/Caldwell_2016/figures/scatterplot")
>
>
> end
>
>
>
> here is the printout from the script when I execute it currently:
>
> Variable: VAL1
> Type: float
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes:   [1]
> Coordinates:
> (0)     -0.45
>
>
> Variable: VAL2
> Type: float
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes:   [1]
> Coordinates:
> (0)     -0.4
>
>
> Variable: z
> Type: integer
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes:   [1]
> Coordinates:
> (0)     3265
>
>
> Variable: i
> Type: integer
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes:   [1]
> Coordinates:
> (0)     0
>
>
> Variable: VAL1
> Type: float
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes:   [1]
> Coordinates:
> (0)     -0.35
>
>
> Variable: VAL2
> Type: float
> Total Size: 4 bytes
>             1 values
> Number of Dimensions: 1
> Dimensions and sizes:   [1]
> Coordinates:
> (0)     -0.3
> fatal:Number of dimensions on right hand side do not match number of
> dimension in left hand side
> fatal:["Execute.c":8640]:Execute: Error occurred at or near line 61 in
> file Albedo_Veg_GFDL_Scatter.ncl
>
>
>
> Thank you for your help,
>
> Sincerely,
>
> Tyler Herrington, MSc
> PhD Student (Climate Science)
> Geography and Environmental Management
> University of Waterloo
>
>
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