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Comparisons

Comparisons (also called relational operators) let programs decide how values relate to each other. They produce boolean results (true/false) and are the basic building blocks for conditionals and filters.

Common comparison operators:

  • == equal to
  • != or ~= not equal to (Matlab uses ~=)
  • < less than
  • > greater than
  • <= less than or equal to
  • >= greater than or equal to
  • 'is' identity comparison (Python only)
  • 'is not' identity negation (Python only)
  • 'in' membership test (Python only)

  • ':=' assignment (not a comparison, but often confused with ==)

  • Comparison

  • Purpose: compare two values and produce a boolean result.
  • Examples: ==, != (or ~=), <, <=, >, >=.
  • Notes: comparison operators are used in conditionals and filtering.
# Basic comparisons
a = 5
b = 3
print(a == b)  # False
print(a != b)  # True
print(a > b)   # True

# Chained comparisons
x = 4
print(1 < x <= 10)  # True (evaluates as 1 < x and x <= 10)

# 'is' checks identity, not equality
s1 = "hello"
s2 = "hello"
print(s1 == s2)  # True (same contents)
print(s1 is s2)  # May be True or False depending on interning (identity)

# Comparing different types can be surprising
print(0 == False)    # True (bool is a subclass of int)
print([] == False)   # False

% Basic comparisons
a = 5;
b = 3;
disp(a == b)   % 0 (false)
disp(a ~= b)   % 1 (true)
disp(a > b)    % 1 (true)

% Element-wise comparisons for arrays
A = [1, 2, 3];
B = [1, 0, 4];
C = A > B;     % [0 1 0]

% Range checks
x = 4;
disp(1 < x && x <= 10) % true (logical short-circuit with scalars)

Gotchas

  1. Floating-point comparisons: exact equality is fragile (e.g., 0.1 + 0.2 == 0.3 may be False). Prefer a tolerance (abs(a-b) < eps).
  2. Identity vs equality: is (Python) checks object identity, not value equality.
  3. Chained comparisons: are evaluated left-to-right but are concise and useful; beware when mixing side-effecting expressions.
  4. Type coercion: some languages coerce types during comparison (Python treats bools as ints; other languages differ).
  5. Array comparisons: in Matlab and NumPy, comparisons on arrays produce element-wise boolean arrays — make sure to reduce with all()/any() when needed.