<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def resample_nn_1d(a, centers):
 """Return one-dimensional nearest-neighbor indexes based on user-specified centers. Parameters a : array-like 1-dimensional array of numeric values from which to extract indexes of nearest-neighbors centers : array-like 1-dimensional array of numeric values representing a subset of values to approximate Returns ------- An array of indexes representing values closest to given array values """

    ix = []
    for center in centers:
        index = (np.abs(a - center)).argmin()
        if index not in ix:
            ix.append(index)
    return ix