Aligning dataset columns in C - c

Question

I have a dataset of two groups: Red and Green, and I want to compare the difference between ratios, but they have to be aligned first.
Original File ( First few rows of 200,000 entries)
A B C D
Red Ratio Green Ratio
1 0.35 1 0.21
2 0.45 2 0.235
3 0.45 3 0.154
4 0.235 4 0.156
6 0.156 5 0.146
7 0.668 6 0.154
8 0.44 7 0.148
9 0.446 8 0.148
10 0.354 9 0.199
11 0.154 10 0.143
12 0.49 12 0.148
After using the code, the values are aligned and the "extras" are delete, and the columns are shifted up.
A B C D
Red Ratio Green Ratio
1 0.35 1 0.21
2 0.45 2 0.235
3 0.45 3 0.154
4 0.235 4 0.156
6 0.156 6 0.154
7 0.668 7 0.148
8 0.44 8 0.148
9 0.446 9 0.199
10 0.354 10 0.143
12 0.49 12 0.148
15 0.146 15 0.87
17 0.113 17 0.113
19 0.44 19 0.448
This is the code I have so far: I am taking difference between A and C to check if they are 0, and adjusting them if they are not.
#include <stdio.h>
int deletemove(char column, int row)
{
// This script would delete the positions mentioned in the arguments, and shift the other values up.
}
int main(void)
{
//Opening input file for read/write
FILE *input;
input=fopen("/full/path/file.xlsx", "r");
if (input == NULL) {printf("error opening input file\n");}
//Store the values from file into an array
int colA[1024];
int colC[1024];
// read contents of columns A and C and store in an array
int ai;
for(ai=1; ai<1024; ai++)
{ fseek(input,ai,SEEK_SET);
colA[ai]=fgetc(input);
}
int ci;
for(ci=1; ci<1024; ci++)
{ fseek(input,ci,SEEK_SET);
colC[ci]=fgetc(input);
}
//Take difference between value of Column A and C to check if they are identical.
int j;
char A,B;
for (j = 1; j < 1024; j++)
{
int check = colA[j] - colC[j]; // check difference between two values in a column
if (check > 0)
deletemove(A,j); //delete values from column C and D
else if (check < 0)
deletemove(B,j); // delete values from column A and B
}
fclose(input); // close files
}
I need help implementing a delete row/column function and reading the values in array.
Also, is storing 200,000 values in an array a feasible method?
Thanks.

Answer 1

is storing 200,000 values in an array a feasible method?
Yes, as long as you don't put those arrays on the stack. Declaring a variable inside a function puts the variable on the stack(1). Contemporary (year 2016) desktops typically limit the stack size to a few megabytes, whereas the main memory is a few gigabytes.
So it's best to put large arrays into main memory. This can be done in a variety of ways:
use a global array, i.e. declare the array outside of any function
use a static array, i.e. declare the array with the static keyword
use a dynamically allocated array, i.e. use malloc to allocate the array
(You could also use a linked list. A linked list has the advantage that it can grow as needed; you don't need to know the space requirements in advance.)
In your case, I would store the ratios in the arrays at the index given by the red/green value. Assuming that ratios are always positive numbers, I would initialize all of the entries in the arrays with -1.0. Then, as you read the file store the ratios at the proper locations in the two arrays. For example, when you read the line
6 0.156 5 0.146
store 0.156 at index 6 in the red array, and store 0.146 at index 5 in the green array.
When all the values have been read from the file, you can simply scan the two arrays, and print the values where both arrays have a non-negative value.
(1) Ignoring oddball systems (e.g. small embedded systems) that don't have a normal stack.