Extract 'url' value from Pandas Series

Question

I have a Pandas DataFrame with the following column called "image_versions2.candidates":

df_myposts['image_versions2.candidates']

That give me:

0      [{'width': 750, 'height': 498, 'url': 'https:/XXX'}]
1                                                    NaN
2      [{'width': 750, 'height': 498, 'url': 'https:/YYY'}]
3      [{'width': 750, 'height': 498, 'url': 'https:/ZZZ'}]

I'm trying to extract the url into a new column called for example 'image_url'.

I can extract a single URL with the following code:

df_myposts['image_versions2.candidates'][0][0]['url']

'https:/XXX'

But with the second row it give me the following error due to de NaN value:

df_myposts['image_versions2.candidates'][1][0]['url']

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-64-3f0532195cb7> in <module>
----> 1 df_myposts['image_versions2.candidates'][1][0]['url']

TypeError: 'float' object is not subscriptable

I'm trying with some type of loop and if condition but I'm having similar error messages:

for i in df_myposts['image_versions2.candidates']:
    if type(i[0]) == 'list':

Wich could be the better option to perform this without dropping NaN rows? I have another column with the Id so I want to mantain the relation id <-> url. Thanks

Answer 1

Use:

df = pd.DataFrame({'a':[1,2,3], 'b':[[{'width': 750, 'height': 498, 'url': 'https:/XXX'}], [{'width': 750, 'height': 498, 'url': 'https:/YYY'}], None]})
# df.dropna(inplace = True) #drop rows with null values
# to preserve rows with NaN, first replace NaN values with a scalar/dict value
df.fillna('null', inplace=True)
df['c'] = df['b'].apply(lambda x: [y['url'] if isinstance(x, list) else 'null' for y in x])
df['c'] = df['c'].apply(lambda x:x[0]) #get only the url from the list

#Output:
    a                        b                                   c
0   1   [{'width': 750, 'height': 498, 'url': 'https:/...   https:/XXX
1   2   [{'width': 750, 'height': 498, 'url': 'https:/...   https:/YYY
2   3                       null                                null

Answer 2

Using @amanb's setup dataframe

df = pd.DataFrame({
    'a':[1,2,3],
    'b':[
        [{'width': 750, 'height': 498, 'url': 'https:/XXX'}],
        [{'width': 750, 'height': 498, 'url': 'https:/YYY'}],
        None
    ]
})

---

You can use str accessor of a pandas.Series to grab the first element of a list. Then use to_dict and from_dict

pd.DataFrame.from_dict(df.b.dropna().str[0].to_dict(), orient='index')

To get

   width  height         url
0    750     498  https:/XXX
1    750     498  https:/YYY

You can use join to add to df

df.join(pd.DataFrame.from_dict(df.b.dropna().str[0].to_dict(), orient='index'))

   a                                                  b  width  height         url
0  1  [{'width': 750, 'height': 498, 'url': 'https:/...  750.0   498.0  https:/XXX
1  2  [{'width': 750, 'height': 498, 'url': 'https:/...  750.0   498.0  https:/YYY
2  3                                               None    NaN     NaN         NaN

Or you can replace the column

df.assign(b=pd.DataFrame.from_dict(df.b.dropna().str[0].to_dict(), orient='index').url)

   a           b
0  1  https:/XXX
1  2  https:/YYY
2  3         NaN

---

My actual recommendation

But my favorite is using pd.io.json.json_normalize in place of the dictionary magic.

df.assign(b=pd.io.json.json_normalize(df.b.dropna().str[0]).url)

   a           b
0  1  https:/XXX
1  2  https:/YYY
2  3         NaN

Answer 3

We can use list comprehension with iterrows here to extract the URL tag:

df.fillna('None', inplace=True)

df['image_url'] = [
    d['image_versions2.candidates']['url'] if d['image_versions2.candidates'] != 'None' else 'None' for idx, d in df.iterrows()
]

print(df)
                          image_versions2.candidates   image_url
0  {'width': 750, 'height': 498, 'url': 'https:/X...  https:/XXX
1                                               None        None
2  {'width': 750, 'height': 498, 'url': 'https:/Y...  https:/YYY
3  {'width': 750, 'height': 498, 'url': 'https:/Z...  https:/ZZZ