function findfirst_propagate_missing(A, x)
if x in A
return findfirst(isequal(x), A)
else
return missing
end
end
Solution 1: Using a custom function
In this solution, we define a custom function called findfirst_propagate_missing that takes in an array A and a value x. It checks if x is present in A using the in operator. If it is, it returns the index of the first occurrence of x using the findfirst function. If x is not present, it returns missing.
A = [1, 2, 3, 4, 5]
x = 3
index = findfirst_propagate_missing(A, x)
println(index) # Output: 3
x = 6
index = findfirst_propagate_missing(A, x)
println(index) # Output: missing
Solution 2: Using the coalesce operator
In this solution, we can use the coalesce operator (??) to propagate the missing value. The coalesce operator returns the first non-missing value from a list of expressions. We can combine the findfirst function with the coalesce operator to achieve the desired behavior.
A = [1, 2, 3, 4, 5]
x = 3
index = findfirst(isequal(x), A) ?? missing
println(index) # Output: 3
x = 6
index = findfirst(isequal(x), A) ?? missing
println(index) # Output: missing
Solution 3: Using the ternary operator
In this solution, we can use the ternary operator (condition ? expression1 : expression2) to propagate the missing value. The ternary operator evaluates the condition and returns expression1 if the condition is true, and expression2 otherwise. We can combine the findfirst function with the ternary operator to achieve the desired behavior.
A = [1, 2, 3, 4, 5]
x = 3
index = x in A ? findfirst(isequal(x), A) : missing
println(index) # Output: 3
x = 6
index = x in A ? findfirst(isequal(x), A) : missing
println(index) # Output: missing
Among the three options, Solution 1 using a custom function is the better choice. It provides a clear and concise way to propagate the missing value without relying on additional operators. It also allows for easy modification or extension of the logic if needed.
