X[i, :, :] = X_data.iloc[row : row + 24]

This code assigns a 3-dimensional array to the variable X, where the first dimension represents the rows, the second dimension represents the columns, and the third dimension represents the depth (or channels). The ":" operator is used to select all rows in the first dimension, while the second and third dimensions are selected using the indices 0 and 1 respectively.

The array is filled with the values of a slice of a pandas DataFrame called X_data, which starts at the index "row" and goes up to (but not including) the index "row + 24" in the first dimension. This means that the slice includes 24 consecutive rows of the DataFrame, starting from the row specified by the "row" variable.

Overall, this code is likely part of a loop that iterates over different values of "row" to create multiple 3-dimensional arrays from different slices of the X_data DataFrame.