best way save data 2D array in java

Question

i've a problem about saving 2d array's value to hardisk. i build 5000x5000 item similarity table (float) and i want to store it because it will be continuesly used. i've tried save them to .txt file by format index1,index2,value+\n and they're growing to 250MB of size (its approx 25million of rows). is there any ways to reduce its size? i would be glad if anyone mind to help me

Answer 1

1. Instead of storing index of each cell i.e. index1 and index2, we can write the size of the matrix at the beginning of the file itself using 2 integers(number of rows & number of columns). Use this information while reading, to know when a row of the matrix is read completely.

2. Instead of writing string value of float, we can use Float.floatToIntBits(float) method to get IEEE-754 representation as an integer and serialize the integer as 4 bytes

This will reduce the size of a 5000 x 5000 matrix to ~ 100MB