Matlab Onramp course notes - Part 3 Plots & Data Import

Plots

Plot Vectors

• Plot two same-length vectors:

  plot(x, y)
  

• Task — plot sample vs mass1:

  plot(sample, mass1)
  

• Specify color/line/marker with a line spec string:

  plot(x, y, "r--o")   % "r--o" = red, dashed, circle markers
  

• Task — plot sample vs mass2 with red stars and no line:

  plot(sample, mass2, "r*")
  

• To overlay plots, use hold on:

  plot(x1, y1)
  hold on
  plot(x2, y2)
  

• Task — hold on; then plot sample vs mass1 with magenta squares and no line:

  hold on
  plot(sample, mass1, "ms")
  

• Stop overlaying:

  hold off
  

• Plotting a single vector uses indices 1:n for x:

  plot(y)
  

• Task — plot v1:

  plot(v1)
  

• Use name-value arguments to set properties (e.g., line width):

  plot(y, LineWidth=5)
  

• Task — plot v1 with LineWidth 3:

  plot(v1, LineWidth=3)
  

• Name-value can follow line spec:

  plot(x, y, "ro-", LineWidth=5)
  

• Task — plot sample vs v1 with red circles, solid line, LineWidth 4:

  plot(sample, v1, "ro-", LineWidth=4)
  

• Try other plotting functions and set properties by name:

  histogram(density, FaceColor="y")
  

• Note: older MATLAB (<R2021a) uses commas and quoted names:

  plot(v1, "LineWidth", 3)
  

Further practice:

plot(v1)
hold on
plot(v2)
hold off
plot(v1, "LineWidth", 3)

Annotate Plots

• Add title:

  title("Plot Title")
  

• Task — add title “Sample Mass” (example full snippet):

  load datafile
  sample = data(:,1);
  density = data(:,2);
  v1 = data(:,3);
  v2 = data(:,4);
  mass1 = density .* v1;
  mass2 = density .* v2;
  plot(sample, mass1, "ms")
  hold on
  plot(sample, mass2, "r*")
  hold off
  title("Sample Mass")
  

• Add axis labels:

  ylabel("Y-Axis Label")
  

• Task — add y-axis label “Mass (g)”:

  ylabel("Mass (g)")
  

• Add a legend:

  legend("a", "b", "c")
  

• Task — legend with “Exp A” and “Exp B” in that order:

  legend("Exp A", "Exp B")
  

• Use variables in annotations (string concatenation):

  bar(data(3,:))
  title("Sample " + sample(3) + " Data")
  

Data Import

• Files panel: browse files. Select + Import Data or double-click to import.
• Double-click MAT -> variables load to workspace.
• Double-click image -> imported as numeric pixel array.
• Double-click spreadsheet -> Import Tool opens (many possible formats).
  • Preview shows import selection in blue.
  • Missing data highlighted orange; default replacement = NaN.
  • Default import = table (columns can have mixed types; rows align).
  • First row detected as headers → used as table variable names.
  • Import Tool infers each variable’s data type.
  • Output variable name comes from file name.
• Click Import Selection to create the workspace variable.

Import Data as a Table

• Extract table variable via dot notation:

  var = table.VariableName
  

Task — Assign elements.Density to a column vector d:

load datafile
elements
d = elements.Density

• To append calculations to a table, assign a new variable:

  data.HeightMeters = data.HeightYards * 0.9144
  

• If data.HeightMeters doesn’t exist, MATLAB creates it.

Task — Multiply elements.Density with elements.Volume1 (element-wise) and save as elements.Mass:

mass = elements.Density .* elements.Volume1
mass
elements.Mass = mass
elements = sortrows(elements, "Mass")

• You can click a table in a live script output to interact (sort, etc.).
• To save edits back to code, click Update Code in the output pane.

• To sort by Mass via the UI: scroll right to Mass column → Sort Smallest to Largest → Update Code.

• Use dot notation to extract table variables; use array indexing to extract rows.

  top3 = elements(1:3,:)
  

• top3 is a table.

  elements(1:3,:)