Python - Creating an array for a series within a loop?

Question

I'd like to add values calculated in a for loop to a series so that it can be its own column in a dataframe. So far I've got this: the y values are from a dataframe named block.

N = 12250
for i in range(0,N-1):
    y1 = block.iloc[i]['y']
    y2 = block.iloc[i+1]['y']
    diffy[i] = y2-y1

I'd like to make diffy its own series instead of just replacing the diffy val on each loop

What kind of object is diffy? A list? A dictionary? A pandas.Series? — dhasson
– dhasson, Commented Jan 3, 2020 at 14:44

Code Different · Accepted Answer · 2020-01-03 15:44:05Z

1

Some sample data (assume N = 5):

N = 5

np.random.seed(42)
block = pd.DataFrame({
    'y': np.random.randint(0, 10, N)
})

   y
0  6
1  3
2  7
3  4
4  6

You can calculate diffy as follow:

diffy = block['y'].diff().shift(-1)[:-1]

0   -3.0
1    4.0
2   -3.0
3    2.0
Name: y, dtype: float64

diffy is a pandas.Series. If you want list, add .to_list(). If you want a numpy array, add .values

answered Jan 3, 2020 at 15:44

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