Find nth value in a matrix and plot on graph
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I have a program that plots a graph and marks 4 dots on each line represening +/- 2mph. I have it figured it out how to place the dots for the beginning and the end but not values 2 through n. I am using the find command but I am having a hard time getting it to find values 2 throught n. Here is the code I am using (will need VEX file that I have attached to run):
Run=6;
i72=zeros([max(Run) 1]); i68=i72; i62=i72; i58=i72; i22=i72; i18=i72; i12=i72; i08=i72;
i=1;
while i<=max(Run)
if i==1
i72(i)=find(VEX>=71 & VEX<=72,1,'first');
i68(i)=find(VEX>67 & VEX<68,1,'first');
i62(i)=find(VEX>61 & VEX<=62,1,'first');
i58(i)=find(VEX>57 & VEX<58,1,'first');
i22(i)=find(VEX<=22,1,'first');
i18(i)=find(VEX<18,1,'first');
i12(i)=find(VEX<=12,1,'first');
i08(i)=find(VEX<8,1,'first');
i=i+1;
elseif i>1 && i~=max(Run)
% Need to Fix
i72(i)=find(VEX<=72,1);
i68(i)=find(VEX<68,1);
i62(i)=find(VEX<=62,1);
i58(i)=find(VEX<58,1);
i22(i)=find(VEX<=22,1);
i18(i)=find(VEX<18,1);
i12(i)=find(VEX<=12,1);
i08(i)=find(VEX<8,1);
i=i+1;
else
i72(i)=find(VEX>=72,1,'last');
i68(i)=find(VEX>68,1,'last');
i62(i)=find(VEX>=62,1,'last');
i58(i)=find(VEX>58,1,'last');
i22(i)=find(VEX>=22,1,'last');
i18(i)=find(VEX>18,1,'last');
i12(i)=find(VEX>=12,1,'last');
i08(i)=find(VEX>8,1,'last');
i=i+1;
end
end
i70=round((i72+i68)/2); i60=round((i62+i58)/2); i20=round((i22+i18)/2); i10=round((i12+i08)/2); % calculate Segment end points: 70, 60, 20, 10 mph
plot(VEX,'b.'); hold on; grid on
plot(i08,VEX(i08),'r*',i12,VEX(i12),'r*',i18,VEX(i18),'r*',i22,VEX(i22),'r*',i58,VEX(i58),'r*',i62,VEX(i62),'r*',i68,VEX(i68),'r*',i72,VEX(i72),'r*')
xlim([0 70000])
Accepted Answer
Is something like this what you're trying to do?
load VEX.mat
% plot VEX
figure
plot(VEX,'b.')
First, identity where VEX has large jumps up or down, from one segment to the next:
jump_threshold = 10;
idx = [true; abs(diff(VEX))>jump_threshold; true];
idx = find(idx)
and plot (for reference) the starts (in green) and ends (in red) of the separate segments:
figure
plot(VEX,'b.')
hold on
plot(idx(1:end-1),VEX(idx(1:end-1)),'g.')
plot(idx(2:end)-1,VEX(idx(2:end)-1),'r.')
Now identify the value (and corresponding index of VEX) in each segment nearest to each of 8, 12, 18, 22, 58, 62, 68, and 72:
vals = [8 12 18 22 58 62 68 72];
NV = numel(vals);
NI = numel(idx)-1;
all_idx = NaN(NI,NV);
all_vals = NaN(NI,NV);
for ii = 1:NI
% subVEX is the data for the ii-th segment:
subVEX = VEX(idx(ii):idx(ii+1)-1);
for jj = 1:NV
% find the element nearest vals(jj) in segment ii
[d,min_idx] = min(abs(subVEX-vals(jj)));
% only store it if it is closer than jump_threshold away from vals(jj)
% (e.g., don't want to match the bottom point of a segment that is
% entirely above 50 to the value 22):
if d <= jump_threshold
all_idx(ii,jj) = min_idx+idx(ii)-1;
all_vals(ii,jj) = subVEX(min_idx);
end
end
end
This is what the indices and VEX values at those points are. (NaNs occur where the nearest point in a segment was further than jump_threshold away from vals(jj)):
disp(all_idx)
disp(all_vals)
Plot the non-NaN elements of those:
figure
plot(VEX,'b.')
hold on
to_plot = ~isnan(all_idx);
plot(all_idx(to_plot),all_vals(to_plot),'r*')
Note that your approach of using find(__,1,'first') and find(__,1,'last') would never work on the interior segments since you are searching in the entire VEX vector. That's why I break VEX into segments first and search each segment individually.
More Answers (1)
Torsten
on 29 Aug 2023
Run = 6;
i72=zeros([max(Run) 1]); i68=i72; i62=i72; i58=i72; i22=i72; i18=i72; i12=i72; i08=i72;
for i = 1:Run
if i==1
i72(i)=find(VEX>=71 & VEX<=72,1,'first');
i68(i)=find(VEX>67 & VEX<68,1,'first');
i62(i)=find(VEX>61 & VEX<=62,1,'first');
i58(i)=find(VEX>57 & VEX<58,1,'first');
i22(i)=find(VEX<=22,1,'first');
i18(i)=find(VEX<18,1,'first');
i12(i)=find(VEX<=12,1,'first');
i08(i)=find(VEX<8,1,'first');
elseif i>1 && i<Run
% Need to Fix
i72(i)=find(VEX<=72,1);
i68(i)=find(VEX<68,1);
i62(i)=find(VEX<=62,1);
i58(i)=find(VEX<58,1);
i22(i)=find(VEX<=22,1);
i18(i)=find(VEX<18,1);
i12(i)=find(VEX<=12,1);
i08(i)=find(VEX<8,1);
else
i72(i)=find(VEX>=72,1,'last');
i68(i)=find(VEX>68,1,'last');
i62(i)=find(VEX>=62,1,'last');
i58(i)=find(VEX>58,1,'last');
i22(i)=find(VEX>=22,1,'last');
i18(i)=find(VEX>18,1,'last');
i12(i)=find(VEX>=12,1,'last');
i08(i)=find(VEX>8,1,'last');
end
end
1 Comment
Ryan McCormack
on 29 Aug 2023
Edited: Ryan McCormack
on 29 Aug 2023
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