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How to find the position of a number in an array?

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Arnab Pal
Arnab Pal el 15 de Feb. de 2018
Comentada: Walter Roberson el 20 de Jul. de 2022
If I have a vector, a = [7 8 8 2 5 6], how do I compute the positions of the value 8?
I expect 2 and 3 or (1,2) and (1,3).

Respuesta aceptada

Walter Roberson
Walter Roberson el 15 de Feb. de 2018
Editada: MathWorks Support Team el 27 de Feb. de 2020
You can use the “find” function to return the positions corresponding to an array element value. For example:
a = [7 8 8 2 5 6];
linearIndices = find(a==8)
linearIndices =
2 3
To get the row and column indices separately, use:
[row,col] = find(a==8)
row =
1 1
col =
2 3
If you only need the position of one occurrence, you could use the syntax “find(a==8,1)”. You can also specify a direction if you specifically want the first or last occurrence, such as “find(a==8,1,’first’). For more information on these options, see find.
  2 comentarios
Arvind Andrew Das
Arvind Andrew Das el 19 de Jul. de 2022
i did the find function, but it gives me the ans vector with all of the values of the array and the results are in true or false for my condition( 0 & 1 ).
Walter Roberson
Walter Roberson el 20 de Jul. de 2022
find() can never return 0. Perhaps you are looking at ans for a different operation?

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Más respuestas (4)

Bhagyesh Shiyani
Bhagyesh Shiyani el 5 de Dic. de 2019
what if i want both 8 positions, any code?
  2 comentarios
Florian Reinbold
Florian Reinbold el 15 de En. de 2020
Hi Bhagyesh
i would suggest this one:
[val, idx] = find(a==8);
It seems to make a great job! :)
Walter Roberson
Walter Roberson el 15 de En. de 2020
This will not return value and index, it will return row and column numbers.

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Ujjawal Barnwal
Ujjawal Barnwal el 7 de Jun. de 2020
a = [7 8 8 2 5 6];
position = find(a==8)

Sorne Duong
Sorne Duong el 21 de Jul. de 2021
a = 1, 3, 6, 9, 10, 15
We know the fourth value is 9, but how to find the fourth value in MATLAB?
  4 comentarios
Torsten el 30 de Mayo de 2022
values = T_03(int_t_03,4)
Reem RA
Reem RA el 30 de Mayo de 2022
Thanks it worked!!!!

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Nilesh Kumar Bibhuti
Nilesh Kumar Bibhuti el 15 de Oct. de 2021
Editada: Walter Roberson el 15 de Oct. de 2021
#include <stdio.h>
#define MAX_SIZE 100 // Maximum array size
int main()
int arr[MAX_SIZE] ,brr[MAX_SIZE] ;
int size, i, toSearch, found ,k=0;
/* Input size of array */
printf("Enter size of array: ");
scanf("%d", &size);
/* Input elements of array */
printf("Enter elements in array: ");
for (i = 0; i < size; i++)
scanf("%d", &arr[i]);
printf("\nEnter element to search: ");
scanf("%d", &toSearch);
for (i = 0; i < size; i++)
if (arr[i] == toSearch)
brr[k] = i+1 ;
printf("%d ",brr[k]);
k++ ;
return 0;
  1 comentario
Walter Roberson
Walter Roberson el 15 de Oct. de 2021
In C, int size should really be size_t size and your scanf() should be using %lu instead of %d . i and k should also be size_t
You should be checking the return status of each scanf() call .
int main()
should be
int main(void)
unless you are using K&R C from before C was standardized.
The user is expecting the positions to be returned, rather than displayed.
You probably shouldn't be assuming integer for the array, but that would be an acceptable limitation if specifically documented.
You do not use or initialize found.

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