Adding arrays to dataframe column

Question

Let's assume I have this dataframe df:

   'Location'  'Rec ID'  'Duration'
0     Houston       126          17
1     Chicago       338        19.3

I would like to add a column with arrays corresponding to my recordings like:

   'Location'  'Rec ID'  'Duration'                           'Rec'
0     Houston       126          17    [0.2, 0.34, 0.45, ..., 0.28]
1     Chicago       338        19.3    [0.12, 0.3, 0.41, ..., 0.39]

When I do the df.set_value() command I get the following error:

ValueError: setting an array element with a sequence.

Take alook http://stackoverflow.com/questions/18646076/add-numpy-array-as-column-to-pandas-data-frame — Hisham Karam, Oct 14 '16 at 05:14

jezrael · Accepted Answer · 2016-10-14T05:41:21.897

I think the easiest is to assign list of lists, only you need same length of lists as length of DataFrame:

arr = [[0.2, 0.34, 0.45, 0.28], [0.12, 0.3, 0.41, 0.39]]
print (arr)
[[0.2, 0.34, 0.45, 0.28], [0.12, 0.3, 0.41, 0.39]]

print (len(arr))
2
print (len(df))
2

df["'Rec'"] = arr
print (df)
   'Location'     'Rec  ID'  'Duration'                    'Rec'
0           0  Houston  126        17.0  [0.2, 0.34, 0.45, 0.28]
1           1  Chicago  338        19.3  [0.12, 0.3, 0.41, 0.39]

If use numpy array, first convert tolist:

arr = np.array([[0.2, 0.34, 0.45, 0.28], [0.12, 0.3, 0.41, 0.39]])
print (arr)
[[ 0.2   0.34  0.45  0.28]
 [ 0.12  0.3   0.41  0.39]]

df["'Rec'"] = arr.tolist()

print (df)
   'Location'     'Rec  ID'  'Duration'                    'Rec'
0           0  Houston  126        17.0  [0.2, 0.34, 0.45, 0.28]
1           1  Chicago  338        19.3  [0.12, 0.3, 0.41, 0.39]

@piRSquared - Thank you. I dont test it. – jezrael Oct 14 '16 at 05:41 — jezrael, Oct 14 '16 at 05:41

Adding arrays to dataframe column

1 Answers1