Conditionally colored line plot

coloring partialy matlab code


Plots vectors x & y using one color for when y is greater than a given threshold value, and another color when y is less than the threshold.


You can optionally specify any standard formatting string that PLOT accepts (eg 'rx:' for a red dotted line with cross markers).


The plotting follows the standard MATLAB PLOT approach of linearly interpolating between data values. The coloring/linestyle changes at y = threshold, even on the interpolated line.

function splitcolorplot(x,y,val,fmt1,fmt2)
% SPLITCOLORPLOT Plots graph split into two colors above and below a given threshold value
% SPLITCOLORPLOT(X,Y,VAL) plots vector Y against vector X, using one
% color when Y > VAL and another when Y < VAL. If VAL is not specified,
% a dividing value of 0 is used.
% As with PLOT, SPLITCOLORPLOT(Y,VAL) plots Y against index numbers,
% instead of X values.
% SPLITCOLORPLOT(X,Y,VAL,FMT1,FMT2) uses standard PLOT formatting strings
% to define the color, linestyle, and marker of the two lines. FMT1
% defines the formatting for the line when Y > VAL.
%
% Acceptable calling syntaxes:
% SPLITCOLORPLOT(Y) [index used for X & VAL = 0]
% SPLITCOLORPLOT(X,Y) [VAL = 0]
% SPLITCOLORPLOT(Y,VAL) [index used for X]
% SPLITCOLORPLOT(X,Y,VAL)
% SPLITCOLORPLOT(X,Y,FMT1,FMT2) [VAL = 0]
% SPLITCOLORPLOT(Y,VAL,FMT1,FMT2) [index used for X]
% SPLITCOLORPLOT(X,Y,VAL,FMT1,FMT2)
%
% Example:
% >> x = 0:0.1:10;
% >> y = sin(4*x);
% >> splitcolorplot(x,y,0.4)
% >> splitcolorplot(y,-0.2,'rx--','k*:')
% Parse inputs (nested function used to set x, y, val, and all necessary
% format options)
checkinputs(nargin)
% Find zero crossings ("zero" = specified level)
if isrow(y)
idx = [0,find(sign(y(2:end)-val)~=sign(y(1:end-1)-val)),lngth];
else
idx = [0;find(sign(y(2:end)-val)~=sign(y(1:end-1)-val));lngth];
end
nidx = length(idx);
% Make an invisible plot -- this means that splitcolorplot has the same
% overwriting behavior as plot
plot(x,y,'visible','off')
% Loop over each segment
for k=2:nidx
% Get first and last indices
k1 = idx(k-1)+1;
k2 = idx(k);
% Choose format, depending on whether y > level or not
fmt = (y(k1)<=val) + 1;
% Plot line segment
line(x(k1:k2),y(k1:k2),'color',clr{fmt},'marker',mrkr{fmt},'linestyle',lntp{fmt})
% Plot linear interpolation to beginning of next line segment
if k<nidx
% Start point is last point of previous line segment
% End point is beginning of next segment
x1 = x(k2);
x2 = x(k2+1);
% Get associated y values
y1 = y(k2);
y2 = y(k2+1);
% Slope
m = (y2-y1)/(x2-x1);
% Find point on line where y = val
x0 = x1 + (val-y1)/m;
% Plot from end of first segment to y = val
line([x1,x0],[y1,val],'color',clr{fmt},'linestyle',lntp{fmt})
% Change formats and plot from y = val to start of 2nd segment
fmt = mod(fmt,2) + 1;
line([x0,x2],[val,y2],'color',clr{fmt},'linestyle',lntp{fmt})
end
end
% Parse all the inputs
function checkinputs(n)
% As long as we have some inputs, get the length of the first
% input (sort out other possible errors later)
if n
lngth = length(x);
end
% Assign values and defaults as best we can (and trust the later
% error checking to sort out any problems)
% How many Romans?!
switch n
% i
case 1
% Single input is vector of y values
y = x;
% Everything else is default
x = 1:lngth;
val = 0;
fmt1 = 'o-';
fmt2 = 'o-';
% ite!
case 2
% Two inputs could be x & y or y & level
% Two equal-sized vectors => x & y
if isequal(size(x),size(y))
val = 0;
% Scalar y => y is level (and x is actually y)
elseif numel(y)==1
val = y;
y = x;
x = 1:lngth;
else
error('x & y must be same size, and level must be a scalar')
end
fmt1 = 'o-';
fmt2 = 'o-';
% if you don't understand these comments, you seriously need
% to watch "Life of Brian"
case 3
% x, y, and level are all set, so set default formats
fmt1 = 'o-';
fmt2 = 'o-';
case 4
% Four inputs => last two are formats
fmt2 = fmt1;
fmt1 = val;
% First two inputs could be x & y or y & level
% Two equal-sized vectors => x & y
if isequal(size(x),size(y))
val = 0;
% Scalar y => y is level (and x is actually y)
elseif numel(y)==1
val = y;
y = x;
x = 1:lngth;
else
error('x & y must be same size, and level must be a scalar')
end
case 5
% Nothing to do here
otherwise
% No.
error('Wrong number of inputs')
end
% Now error-check the hell out of the x, y, val, fmt1, & fmt2 that
% we ended up with.
if ~isequal(size(x),size(y))
error('x & y must be same size')
elseif ~isvector(x)
error('x & y must be vectors')
elseif ~isscalar(val)
error('Level must be a scalar')
elseif ~isnumeric(x) || ~isnumeric(y) || ~isnumeric(val)
error('x, y, and level must be numeric')
elseif ~ischar(fmt1) || ~ischar(fmt2)
error('Formats must be strings')
end
% Parse and deconstruct the format strings
% Look for color specifiers first
[clr{1},fmt1] = getcolor(fmt1,'b');
[clr{2},fmt2] = getcolor(fmt2,[0 0.5 0]);
% And now for markers
[mrkr{1},fmt1] = getmarker(fmt1);
[mrkr{2},fmt2] = getmarker(fmt2);
% And what's left is a linestyle
fmt1 = getlnstyle(fmt1,mrkr{1});
fmt2 = getlnstyle(fmt2,mrkr{2});
lntp = {fmt1,fmt2};
end
function [c,fmt] = getcolor(fmt,def)
% Possible values
clrs = '[bgrcymkw]';
% See if fmt1 includes any of the possible values
idx = regexp(fmt,clrs);
if isempty(idx)
% No? Set default
c = def;
else
% Yes? Cool, that's the color. Remove all color specifiers
% from the string.
if numel(idx)~=1
warning('SPLITCOLORPLOT:multipleColors',...
'More than one color detected')
end
c = fmt(idx(1));
fmt(idx) = [];
end
end
function [m,fmt] = getmarker(fmt)
marks = '[.ox+*sdv^<>ph]';
idx = regexp(fmt,marks);
% Special case: if there's a dot (.), we need to make sure it
% isn't part of the linestyle specifier -.
if ~isempty(regexp(fmt,'.','once'))
% Go through all possibilities (.s) in reverse order --
% reverse because we will remove any that shouldn't be there,
% and that will mess up the indexing
for j=length(idx):-1:1
% If there's a - in front of the ., remove it from the
% list of possibilities (it's a line specifier, not a
% marker)
if idx(j)>1 && strcmp(fmt(idx(j)-1:idx(j)),'-.')
idx(j) = [];
end
end
end
% OK, now go through and work out marker
if isempty(idx)
% Nothing given? Set default
m = 'none';
else
% Otherwise, that's the marker. Remove all marker specifiers
% from the string.
if numel(idx)~=1
warning('SPLITCOLORPLOT:multipleMarkers',...
'More than one marker type detected')
end
m = fmt(idx(1));
fmt(idx) = [];
end
end
function fmt = getlnstyle(fmt,m)
% If there's nothing left, no linestyle was specified. However,
% the depends on whether a marker was given
if isempty(fmt)
% No marker (and no linestyle) => default solid line
if strcmp(m,'none')
fmt = '-';
% Marker given but no linestyle => no line (just marker)
else
fmt = 'none';
end
% Something was specified. Was it valid?
elseif ~ismember(fmt,{'-','--',':','-.'})
error('Unknown format specification')
end
end
end