def get_stride_frequencies(stride_desc):
    """
    Compute the frequencies for each secondary structure element.

    Parameters
    ----------
    stride_desc : list of (str, str, float, float, float)
        The Stride description.

    Returns
    -------
    freqs : dict of str -> int
        The dictionary mapping each code to its frequency.
    """
    freqs = {}
    for sd in stride_desc:
        code = sd[1]
        if code not in freqs:
            freqs[code] = 0
        freqs[code] += 1
    return freqs