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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ND_all_available():
 """Return an array of available nominal diameters. NDs available are those commonly used as based on the 'Used' column in the pipedb. """

    ND_all_available = []
    for i in range(len(pipedb['NDinch'])):
        if pipedb.iloc[i, 4] == 1:
            ND_all_available.append((pipedb['NDinch'][i]))
    return ND_all_available * u.inch