Select the first element that is even:

Return the index of the selected element:

Give the default x when no even numbers are found:

Use the operator form of SelectFirst:

SelectFirst operates on values in an Association:

Use SelectFirst with a Tabular object:

Select the first number between 9 and 99 that equals 1 modulo both 3 and 5:

Select the first 4-tuple that reads the same in reverse:

Find the first 3×3 matrix of 0s and 1s that has determinant 1:

Select an eigenvalue that lies within the unit circle:

Find the first built-in Wolfram Language object whose name is at least 36 characters long:

Select the first numeric quantity from a product:

Find the position of the first prime in a random sample from a PoissonDistribution:

Find the distribution of positions of first primes:

The default value is only evaluated if needed:

SelectFirst returns only the first match:

Select returns all matches:

SelectFirst can be implemented with a combination of Select and Replace:

SelectFirst is similar to FirstCase except that it uses a function instead of a pattern:

Select the first list that has a sum of elements less than 10:

Use FirstCase to get the same result:

The head of the input expression is not preserved: