TypeError: Object of type 'ndarray' is not JSON serializable

Question

knownEmbeddings = []
knownNames = []

for (i, imagePath) in enumerate(imagePaths):
    ## SOME CODE
    knownNames.append(name)
    knownEmbeddings.append(vec.flatten())


data = {"embeddings": knownEmbeddings, "names": knownNames}

f = open('file.json', "wb")
f.write(json.dumps(data, indent=4))
f.close()

Here is the data looks like:

{'embeddings': [array([ 2.23568859e-04, -4.08176295e-02, -1.56606492e-02, -1.40566211e-02,
        5.53448219e-04,  1.34807974e-01,  2.10583732e-02, -7.99260102e-03,
        8.04360434e-02,  2.51036473e-02, -2.45967298e-03,  8.73192959e-03,
        1.08047323e-02,  8.02712217e-02,  6.31465465e-02,  9.41963419e-02],
      dtype=float32), array([-5.54675907e-02,  1.19409459e-02, -3.03599555e-02, -2.86714472e-02,
        6.26528710e-02,  1.25348523e-01, -2.16291733e-02, -4.60545160e-02,
        6.25465512e-02, -7.61162862e-02,  4.28330414e-02,  8.57844874e-02,
        3.75184380e-02, -8.10878351e-02, -8.96525383e-02,  8.15552175e-02,
       -9.75750014e-02, -8.24848488e-02,  9.30746570e-02,  1.71318889e-01,
        1.00642473e-01,  5.39120510e-02,  1.12627009e-02,  1.40678780e-02,
       -4.41719554e-02,  1.03237763e-01,  4.38372791e-02,  7.53327608e-02],
      dtype=float32), array([-0.03736538, -0.0485549 , -0.0976112 , -0.06195155,  0.00269726,
        0.07389018, -0.07325964,  0.06653353, -0.04690087, -0.02606474,
        0.03597135,  0.06904668,  0.02198682, -0.06437466, -0.04554454,
        0.01083081, -0.06293067,  0.07047471,  0.02824293, -0.15522538,
       -0.01900602,  0.10689866, -0.07408814, -0.0419201 ,  0.10475922,
        0.04784475, -0.09085421, -0.20360689,  0.08321641,  0.08441921,
        0.01941148,  0.03566081, -0.05956643,  0.005247  , -0.03989819,
        0.02512971,  0.00458561,  0.13706829], dtype=float32), array([ 7.87236728e-03,  5.65276742e-02, -7.17918649e-02, -1.84332877e-02,
        1.28411269e-02,  2.85971135e-01,  3.13642109e-03,  2.48481780e-02,
       -9.48547944e-02,  2.89725009e-02,  4.33916636e-02,  9.01726633e-02,
        4.36290540e-02, -1.02897413e-01,  2.22285688e-02, -5.19381762e-02,
        1.52556881e-01, -1.25146270e-01,  3.18806712e-03, -2.51053665e-02,
       -4.36606398e-03,  7.19061792e-02,  4.66747172e-02,  8.13280419e-02],
      dtype=float32), array([ 0.09142991, -0.05100765, -0.09615178, -0.03553161,  0.11363017,
        0.19886988,  0.11280693,  0.0229619 , -0.0220201 , -0.01211688,
        0.07489388,  0.0802715 ,  0.16185616, -0.0904082 ,  0.0025941 ,
        0.12167819, -0.07357537, -0.01442344, -0.01343578,  0.16952834,
        0.03366659, -0.0534111 , -0.01595308,  0.15053654, -0.07398864,
        0.04694209, -0.06523879,  0.01342433], dtype=float32), array([-0.05331187,  0.08159426, -0.01742208,  0.00992642, -0.01155609,
        0.25759327, -0.00505029, -0.09290393,  0.01588799, -0.00478396,
        0.08572742, -0.05053008,  0.05197625,  0.1267016 ,  0.15398905,
        0.13668832, -0.13869229,  0.02502107, -0.04443422, -0.05987623,
        0.14948404,  0.03311499,  0.12621029], dtype=float32), array([ 0.1219558 , -0.0371135 , -0.13762642,  0.00431138,  0.20073804,
        0.09986125,  0.21617071,  0.02764285, -0.1352063 ,  0.02268699,
       -0.04734468,  0.10888206,  0.13558514, -0.00319178,  0.02979032,
        0.03558976, -0.07293532, -0.05351996, -0.02449711,  0.1459181 ,
       -0.00320001,  0.01020296, -0.05007216,  0.05868218, -0.03522768,
       -0.01064874, -0.0732395 , -0.05393502], dtype=float32), array([ 0.10833652,  0.08779355, -0.15162815, -0.03925862,  0.08713786,
        0.2850307 ,  0.13499181,  0.01792248, -0.1405847 ,  0.08626581,
        0.02001712, -0.06957201, -0.00727825,  0.01650161,  0.11886367,
        0.07897119, -0.14108546,  0.03840445,  0.05881708,  0.03361814,
       -0.0106756 , -0.04287936, -0.06621028], dtype=float32), array([ 4.90577929e-02,  9.13119391e-02, -2.76884548e-02, -5.19143604e-02,
        1.50506735e-01,  1.86451554e-01,  9.94046330e-02, -7.73873506e-03,
       -1.91362634e-01,  4.69892733e-02, -5.67045361e-02,  2.81608831e-02,
        5.74332848e-02, -9.09122005e-02,  1.46917075e-01,  4.63287433e-04,
        4.22818065e-02, -2.01395284e-02,  1.31114023e-02, -6.61114752e-02],
      dtype=float32), array([ 1.13848910e-01,  1.16239523e-03, -6.73869327e-02,  8.96331621e-05,
        6.71111122e-02,  2.01299891e-01,  1.76381439e-01,  1.44544961e-02,
       -1.36415318e-01, -3.18108648e-02, -3.51585075e-02,  1.24862537e-01,
        6.54390603e-02, -1.79662079e-01,  8.39038659e-03, -6.52492717e-02,
       -4.79320846e-02, -4.05376814e-02, -1.82695538e-02,  1.35992825e-01,
        6.97307214e-02, -5.41270301e-02,  3.14575769e-02,  2.86752880e-02,
        9.04180668e-03,  3.10734902e-02, -3.88299376e-02, -7.43401796e-02],
      dtype=float32), array([ 0.09236415,  0.05246023, -0.03693461,  0.05469636,  0.05779893,
        0.13331857,  0.21085702, -0.01114039, -0.09325632,  0.07158454,
        0.03167493,  0.13376454,  0.13156445, -0.12092946, -0.02573274,
       -0.05352074,  0.00177706,  0.05248505, -0.07331309,  0.06653137,
       -0.02102634,  0.00347302, -0.19828801, -0.08791062,  0.05434143,
        0.07060813, -0.09335811, -0.04778329, -0.02983012,  0.1595401 ,
        0.01018381, -0.04852933, -0.03336967,  0.02886004,  0.05975606,
        0.0974864 , -0.00946077, -0.06796782], dtype=float32), array([ 7.70701468e-02,  2.34568515e-03, -1.22838043e-01,  6.06604481e-05,
        1.08674861e-01,  2.40898028e-01,  7.23511800e-02, -4.14036550e-02,
       -1.20636895e-01, -2.74732499e-03, -1.84729435e-02,  6.18617162e-02,
        8.97722915e-02, -1.62845016e-01, -1.34318219e-02,  5.31670935e-02,
       -8.27090293e-02, -1.22121066e-01,  1.53016988e-02,  1.22807577e-01,
       -1.36648446e-01,  1.32556446e-02, -8.84201974e-02,  8.29895660e-02,
        5.18502928e-02, -7.32250437e-02,  6.30651340e-02, -9.98577196e-03,
       -4.71815281e-02,  6.02727272e-02, -7.98970908e-02, -2.12689787e-02],
      dtype=float32)], 'names': ['adam', 'adam', 'adam', 'adam', 'adam', 'adam', 'bhalla', 'bhalla', 'bhalla', 'bhalla', 'bhalla', 'bhalla']}

I need to save it in json file. When I debug, the data shows as type dict so I used json.dumps(data) to save it in json file but it is throwing below error:

TypeError: Object of type 'ndarray' is not JSON serializable

How can I resolve it

Answer 1

Adding from previous answers and this post, you can do something like this:

class NumpyEncoder(json.JSONEncoder):
    """ Special json encoder for numpy types """
    def default(self, obj):
        if isinstance(obj, (np.int_, np.intc, np.intp, np.int8,
                            np.int16, np.int32, np.int64, np.uint8,
                            np.uint16, np.uint32, np.uint64)):
            return int(obj)
        elif isinstance(obj, (np.float_, np.float16, np.float32,
                              np.float64)):
            return float(obj)
        elif isinstance(obj, (np.ndarray,)):
            return obj.tolist()
        return json.JSONEncoder.default(self, obj)

Then you can call

import numpy as np
import json
operation = json.dumps(data, cls=NumpyEncoder)

In case you are working with a dictionary and want to save the modified dictionary but receiving a similar error

'TypeError: Object of type intc is not JSON serializable'

you can use

dumped = json.dumps(data, cls=NumpyEncoder)
with open('json_file_path.json', 'a') as f:
    f.write(dumped + '\n') 

The code ensure the save json file does not contain \ splashes as stated in here

Answer 2

data is a dict indeed, but it contains lists of ndarrays, which need to be serialized too, and are not (natively) serializable.

What you need here is to provide your own JSONEncoder that knows how to deal with ndarray (turning them into lists as suggested by bharatk being the most obvious solution).