How to solve a task within Machine Learning Onramp Course?

Hello everyone

I hope to get help regarding the following inquiry:

I am doing the Machine Learning Onramp Course. Currently I am in the section: Engineering Features Automate Feature Extraction (Create a Feature Extraction Function).

I am following the next instruction to complete the task:

load sampleletters.mat
letter = b1;

aratio = range(letter.Y)/range(letter.X)
idxmin = islocalmin(letter.X,"MinProminence",0.1);
numXmin = nnz(idxmin)
idxmax = islocalmax(letter.Y,"MinProminence",0.1);
numYmax = nnz(idxmax)
dT = diff(letter.Time);
dXdT = diff(letter.X)./dT;
dYdT = diff(letter.Y)./dT;
avgdX = mean(dXdT,"omitnan")
avgdY = mean(dYdT,"omitnan")
corrXY = corr(letter.X,letter.Y,"rows","complete")

featurenames = ["AspectRatio","NumMinX","NumMaxY","AvgU","AvgV","CorrXY"];

Task 1

Make a table from the features stored in the variables aratio, numXmin, numYmax, avgdX, avgdY, and corrXY by using the table function. Store the result in a variable named feat.

feat = table(aratio,numXmin,numYmax,avgdX,avgdY,corrXY,'VariableNames',featurenames)

Task 2

Recreate the table of features feat, but with the table variable names from the array featurenames.

feat = table(aratio,numXmin,numYmax,avgdX,avgdY,corrXY,'VariableNames',featurenames)

Task 3

At the end of the script, add a local function named extract that takes a single variable, letter, as input and returns a table of features, feat, as output. Copy the code from the beginning of the script, from after letter = b1 to Task 1, and from Task 2 to make the body of the function. Test your function by calling it with b2 as input. Store the result in a variable named featB2.

featB2 = extract(b2)

I got the error

Error using extract (line 6)

Not enough input arguments.

I will really appreciate your cooperation.

Answer 1

[Walter Roberson]

You did not add a local function named extract to your file. A "local function" is one that is placed at the end of your code, starting with the keyword function . (In most cases, you also need an end statement corresponding to the function keyword)

With you not having added a local function named extract to your code, your code was accidentally invoking the MATLAB extract function.