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Get all array elements with true values in Julia | Array findall() Method
  • Last Updated : 23 Mar, 2020

The findall() is an inbuilt function in julia which is used to return a vector of indices or keys of the all true values from the specified array A. If such true values are not present in the array, return an empty array. Here values of index or key start from 1 i.e, for index of 1st element is 1, index of 2nd element is 2 and so on.

Syntax:
findall(A)
or
findall(f::Function, A)

Parameters:

  • A: Specified array
  • Function: Determines whether something is true or false based on the specified arguments

Returns: It returns a vector of indices or keys of the all true values from the specified array A. If such true values are not present in the array, return an empty array.

Example 1:



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# Julia program to illustrate 
# the use of Array findall() method
   
# Finding index of all true values from 
# the 1D array A
A = [false, true, true, false]
println(findall(A))
   
# Finding index of all true values from 
# the 2D array B of size 2 * 2
B = [false false; true false]
println(findall(B))
   
# Finding index of all true values from 
# the 3D array C of size 2 * 2*2
C = cat([false false; true false], 
        [false true; true false],
        [true false; true true], dims = 3)
println(findall(C))

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Output:

Example 2:

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# Julia program to illustrate 
# the use of Array findall() method
   
# Finding index of all even values from 
# the 1D array A
A = [1, 2, 5, 7]
println(findall(iseven, A))
   
# Finding index of all odd values from 
# the 2D array B of size 2 * 2
B = [3 5; 6 7]
println(findall(isodd, B))
   
# Finding index of all odd values from 
# the 3D array C of size 2 * 2*2
C = cat([6 2; 6 4], [5 6; 2 8], 
        [2 10; 11 1], dims = 3)
println(findall(isodd, C))

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Output:




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