Error using bar (line 159) X must be same length as Y. Error in Lab3_Q1234 (line 60) bar(x, y);

% Author Name: Foredul Islam
% Student ID: U0000008501
%Question_1.Since the data logs do not contain samples with a fixed period, the samples will be weighted based onthe amount
%of time spent in each sample. To facilitate this, create a new array in from the input file such that has in each row:
% • the time stamp from the data log file
% • the elapsed time since the previous sample, which is time[n]-time[n-1]
% • the averaged continuous readings, which is (value[n]+value[n-1])/2, 
%or the unmodified discrete value (just the Gear Position)Your new array will have one fewer row than the input file 
%since the log file’s rows 1 and 2 are used to calculate the first row in the new array, rows 2 and 3 are used for the 
%second row, and so on. This array must be returned by the function, but it does not need to be output or captured as a 
%deliverable. (Hint: when calling the function, end the line with a ‘;’ so 100,000’s of rows doesn’t print to the command 
%window.)

f=readmatrix("datalog1.csv");
f(1:10,:)
len=size(f,1)
N=zeros(len-1,8);



N(:,[1 6])=f(2:end,[1,5]);
N(:,2)=f(2:end,1)-f(1:(len-1),1);
N(:, [3 4 5 7 8])=(f(2:len, [2 3 4 6 7])+f(1:(len-1), [2 3 4 6 7]))/2;

N(1:10,:)

%Question 2.	Using the weighted data from step 1 to calculate the overall weighted average for Fuel Economy. 
%This result must be printed to the Command Window with an appropriate message. 

data = N(:,2);
f_economy = N(:,5);
avg_economy = sum(f_economy.*data)/sum(data)

%Question3.	Since the value in step 2 accounts for time spent sitting still at stop lights and stop signs, it may be 
%interesting to see what the vehicle is capable of if traffic is not an issue. Calculate the weighted average for Fuel
%Economy excluding all samples with a Vehicle Speed of 0 mph. This result must be printed to the Command Window with 
%an appropriate message. 

weight = N(N(:,8)>0,:);
weight_data = weight(:,2);
weight_f_economy = weight(:,5);
weght_avg_economy = sum(weight_f_economy.*weight_data)/sum(weight_data)


% Question_4

 maxim_sp = max(N(:,8));
 
 y = zeros(1, ceil(maxim_sp/5));

 for i = [0:5:ceil(maxim_sp)]
     n = N( (N(:,8)<(i+5)) & (i<=N(:,8)), :);
     data = n(:,2);
     fuel_economy = n(:,5);
     avg_economy = sum(fuel_economy.*data)/sum(data);
     x(floor(i/5)+1) = i;
     y(floor(i/5)+1) = avg_economy;
 end
 
 bar(x, y);
 title("weighted Average Fuel Economy in 5 MPH Increments")
 xlabel("Vehicle Speed (MPH)")
 ylabel("Weighted Average Fuel Economy")

Answer 1

[Walter Roberson]

You preallocate y but not x. If you got the preallocation wrong then the two can end up different sizes. And you did get the preallocation wrong.

Suppose maxim_sp is 5. ceil(5/5) is 1 so you would preallocate y as zeros(1,1). Then the loop is 0:5:ceil(5) which is 0:5:5 which contains 0 and 5 which is length 2, not 1.

You need to make sure that the size allocated for x and y are the same and match the number of loop iterations.

Hint:

ivals = 0:5:ceil(maxim_sp)
numi = length(ivals)
y = zeros(1,numi)

[Foredul Islam]

Thank you