How to modify a Python JSON objects array

Question

Let's assume the following :

sp_sample=[{"t":1434946093036,"v":54.0},{"t":1434946095013,"v":53.0},{"t":1434946096823,"v":52.0}

I wish I could get the following result :

sp_sample=[{"t":1434946093036,"v":5400.0},{"t":1434946095013,"v":5300.0},{"t":1434946096823,"v":5200.0}

In other words, I wish I could iterate through the array and multiple v by a 100 factor.

The following only performs the multiplication on the first item, ie yields 54000 :

for i, a in enumerate(sp_sample):
    a[i]['v'] =  a[i]['v'] * 100

The sp_sample is of type tuple. Using the following yields the whole array, which is not what I expect :

print sp_sample[0]

Also, tried printing sp_sample :

print sp_sample

Which returns the following (replaced the ....... for brevity) :

([{'t': 1434946093036, 'v': 54.0}, {'t': 1434946095013, 'v': 53.0}, {'t': 1434946096823, 'v': 52.0}, {'t': 1434946098612, 'v': 52.0}, {'t': 1434946100400, 'v': 51.0}, {'t': 1434946102372, 'v': 49.0},........, {'t': 1434947987823, 'v': 15.0}, {'t': 1434947989851, 'v': 12.0}, {'t': 1434947991899, 'v': 10.0}, {'t': 1434947993744, 'v': 5.0}, {'t': 1434947995599, 'v': 0.0}, {'t': 1434947997455, 'v': 0.0}, {'t': 1434947999494, 'v': 0.0}, {'t': 1434948001542, 'v': 0.0}, {'t': 1434948003417, 'v': 0.0}, {'t': 1434948005264, 'v': 0.0}, {'t': 1434948007120, 'v': 0.0}],)

print type(sp_sample) returns :

mhawke · Accepted Answer · 2015-11-10 10:05:34Z

8

Simply iterate over the list and update the dictionaries as you go:

sp_sample = [{"t":1434946093036,"v":54.0},{"t":1434946095013,"v":53.0},{"t":1434946096823,"v":52.0}]

for d in sp_sample:
    d['v'] *= 100

>>> print(sp_sample)
[{'t': 1434946093036, 'v': 5400.0}, {'t': 1434946095013, 'v': 5300.0}, {'t': 1434946096823, 'v': 5200.0}]

This will bind in turn each dictionary in list (tuple?) sp_sample to d, which you then update in place. You do not need to use enumerate().

Note that you really need to multiply by 100, not 10000, to achieve the output that you have shown.

Update

sp_sample is actually a tuple with a list of dictionaries as its only item. So you need to access the list in the tuple like this:

sp_sample = ([{"t":1434946093036,"v":54.0},{"t":1434946095013,"v":53.0},{"t":1434946096823,"v":52.0}],)

for d in sp_sample[0]:    # N.B. access first item of tuple
    d['v'] *= 100
>>> print(sp_sample)
[{'t': 1434946093036, 'v': 5400.0}, {'t': 1434946095013, 'v': 5300.0}, {'t': 1434946096823, 'v': 5200.0}]

Or, since the tuple contains only a single item you could just get rid of the tuple by:

sp_sample = sp_sample[0]
for d in sp_sample:
    d['v'] *= 100

edited Nov 10, 2015 at 10:05

answered Nov 10, 2015 at 8:47

mhawke

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5 Comments

SCO Over a year ago

Python returns the following : Traceback (most recent call last): File "./gear_add_10.py", line 20, in <module> d['v'] *= 100 TypeError: list indices must be integers, not str

mhawke Over a year ago

Then sp_sample is a list of lists, not a list of dictionaries as one would expect from the sample data in your question. Perhaps you could try printing the value of sp_sample before entering the update loop and double check the data types.

mhawke Over a year ago

If sp_sample is in fact a list of lists, then you would need to change your code to for item in sp_sample: item[1] *= 100`.

SCO Over a year ago

I have the feeling that according to Python, the array is one item long, it looks like it unable to understand embedded objects.

mhawke Over a year ago

From the update to your question you seem to have a tuple with a single list item, which is a list of dictionaries. So changing your code to: for d in sp_sample[0]: d['v'] *= 100 should fix it.

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