C data format redoing - c

Question

I have data stored as
float testdata3[][7] = {
{171032, 0.4448, -0.3032, -0.7655, -1.3428, 13.5803, -73.0743},
{172292, 0.0099, 0.1470, -0.7301, -17.2272, 7.0038, -11.7722},
{173547, 0.0576, 0.1333, -0.8163, -2.7847, -9.5215, 8.1177 },
...
}
where I am only interested in the second, third and fourth indexes. How can I create a function where it would return for example first, second and third index as their own table from the testdata I have.
For example
testdata_x = {0.4448, 0.099, 0.0576, ...}
testdata_y = {-0.3032, 0.1470, 0.1333, ...}
testdata_z = {-0.7655, -0.7301, -0.8163, ...}
Help would be much appreciated. I am trying to read sensor values from test data and im only interested in acceleration values in x, y and z directions.

Answer 1

You didn't post any code so I'm going to be a bit more vague than normal.
If we create an array of 7 elements such as: int arr[7] = {1, 2, 3, 4, 5, 6, 7};
Accessing the 2nd, third, and 4th elements is as simple as arr[1], arr[2], arr[3] respectively.
That should help with gleaning the data from the existing arrays, but as for making your new array. I don't see any reason to use a multidimensional array instead of 3 regular arrays. All you need to do from here is find out the amount of arrays in testData in order to know how much to allocate and you should be on your way.

Answer 2

So you want to transpose a matrix? then just iterate in the reverse order
#include <stdio.h>
int main(void)
{
double arr[][7] = {
{171032, 0.4448, -0.3032, -0.7655, -1.3428, 13.5803, -73.0743},
{172292, 0.0099, 0.1470, -0.7301, -17.2272, 7.0038, -11.7722},
{173547, 0.0576, 0.1333, -0.8163, -2.7847, -9.5215, 8.1177},
};
#define ROWS sizeof arr / sizeof arr[0]
#define COLS sizeof arr[0] / sizeof arr[0][0]
double test[COLS][ROWS]; /* 7 x 3 */
for (size_t i = 0; i < COLS; i++) {
for (size_t j = 0; j < ROWS; j++) {
test[i][j] = arr[j][i];
}
}
return 0;
}

Answer 3

I don't know what you are looking for but here are several approaches starting from easiest one:
1) You can directly assign a value using indexes to the new array
2) If you need function you can allocate new array inside it assign all
values and return it from a function
It's supposed that indexes never change for x,y,z.
#include <stdio.h>
#include <stdlib.h>
enum
{
X,
Y,
Z
};
float testdata3[][7] = {
{171032, 0.4448, -0.3032, -0.7655, -1.3428, 13.5803, -73.0743},
{172292, 0.0099, 0.1470, -0.7301, -17.2272, 7.0038, -11.7722},
{173547, 0.0576, 0.1333, -0.8163, -2.7847, -9.5215, 8.1177 },
};
float *get_dataa(int coordinate)
{
float *data;
switch(coordinate) {
case X:
data = malloc(sizeof(float) * 3);
data[0] = testdata3[0][1];
data[1] = testdata3[1][1];
data[2] = testdata3[2][1];
return data;
default:
return NULL;
}
}
int main(void)
{
/* first way */
float testdata_X[] = { testdata3[0][1], testdata3[1][1], testdata3[2][1] };
printf("Test number 1 for X %0.4f, %0.4f, %0.4f\n", testdata_X[0], testdata_X[1], testdata_X[2]);
/* second */
float *testdata_xX = get_dataa(X);
printf("Test number 2 for X %0.4f, %0.4f, %0.4f\n", testdata_xX[0], testdata_xX[1], testdata_xX[2]);
free(testdata_xX);
return 0;
}
output:
Test number 1 for X 0.4448, 0.0099, 0.0576
Test number 2 for X 0.4448, 0.0099, 0.0576