In Julia, you can use the findfirst() function to get the index of the first occurrence of an element in an array. Here is an example:
# defining an array
my_array = [2, 4, 6, 8, 10]
# finding the index of the first occurrence of '6'
index = findfirst(x -> x==6, my_array)
# printing the result
println("The index of '6' is $index")
# output: The index of '6' is 3
In the above example, the findfirst() function takes two arguments: the first is a function that defines the condition for the element we want to find and the second is the array in which we want to look for this element.
The function x -> x==6 is a lambda function in Julia that checks if a given element x is equal to 6. It is passed as the first argument to the findfirst() function to define the condition for which element we are looking for. When executed, this code outputs the index of the first occurrence of 6 in the array my_array, which is 3.
You can also use the findall() function to get the indices of all occurrences of an element in an array. Here is an example:
# defining an array
my_array = [2, 4, 6, 8, 10, 6]
# finding the index of all occurrences of '6'
indices = findall(x -> x==6, my_array)
# printing the result
println("The indices of '6' are $indices")
# output: The indices of '6' are [3, 6]
In the above example, the findall() function finds all the indices of the elements that satisfy the condition x -> x==6. The result is a vector of indices [3, 6], corresponding to the indices of both occurrences of 6 in the array my_array.