Python：如何对列中字典列表的值求和

Question

I have a DataFrame like this:

timestamp                                asks
2022-01-01 00:00:00                 [{'price':'0.99', 'size':'12311'},{'price':'0.991', 'size':'20013'}]
2022-01-01 01:00:00                 [{'price':'0.99', 'size':'3122'},{'price':'0.991', 'size':'43221'}]
...

What I want to do is sum up the values of size for each timestamp to get the following DataFrame:

timestamp                 asks
2022-01-01 00:00:00       32324
2022-01-01 01:00:00       46343
...

ie 12311+20013= 32324 .

How can this be done (using pandas ideally)?

Answer 1

df["asks"] = df["asks"].explode().str["size"].astype(int).groupby(level=0).sum()

• get each dictionary on a separate row
• get the "size" key's value for each of them
  • due to ducktyping, .str[...] works on anything that supports __getitem__ which a dictionary does
• convert to integers and unexplode

to get

>>> df

             timestamp   asks
0  2022-01-01 00:00:00  32324
1  2022-01-01 01:00:00  46343