How to query a pandas DataFrame using an array of tuples ?

Question

I have a pandas DataFrame with the following structure:

And I have an array of tuples

arr_tuples = [(0,3),(1,1),(1,3),(2,1)]

Each tuple in the array represent the row and column index of the above dataframe respectively.

I can find all the values in the data frame for the indices in arr_tuples using for loop like this:

value_array = []
for item in arr_tuples:
    row = item[0]
    col = item[1]
    value = df.iloc[row,col] # I also tried df.get_value here with similar result 
    value_array.append(value)

But this seems to be a very slow method. If there are a lot of tuples in my arr_tuples, this will take a long time.

Is there a better and faster way to achieve the same ? Is there any way in pandas where I can use a list/array of tuples (containing row and column index) to get values in a dataframe ?

Answer 1

You can use pd.DataFrame.lookup with some zip and unpacking trickery

df.lookup(*zip(*arr_tuples))

array([ 4,  5,  7, 12])

---

• list(zip(*arr_tuples)) creates two tuples out of the list of tuples

  [(0, 1, 1, 2), (3, 1, 3, 1)]
  

• Well that's perfect because the first tuple are indices and the second are columns. That's what pd.DataFrame.lookup accepts as arguments. So if I unpack those, it'll just work

  df.lookup(*zip(*arr_tuples))
  
  array([ 4,  5,  7, 12])