将多个函数应用于 Pandas DataFrame 返回几列的有效方法

Question

I have a large datasource in which I am trying to enrich the data by creating some calculated columns.

The data source is close to 4 Million rows and I am pulling the data in chunks of 100,000

for field in fields:
   operation_start = time.time()
   print(f"Operation {y+1}")
   chunk[field] = chunk.apply(operations[y], axis = 1)                    
   print("Operation completed in " + str(round(time.time()-operation_start,2)) + " seconds")
   operation_start = time.time()
   y = y +1

The for loop runs for 9 functions I have defined, each one returning a value for a new column.

Is there a more efficient way in which I capture all the new fields at once, applying everything at once instead of one by one? One important remark is that there are a pair of the functions that need the value created by other functions

I have tried pandarallel but it makes the process even slower.

EDIT:

I managed to make a function and use pandarallel following the info here Apply multiple functions to multiple groupby columns however it does not append the new columns

def Operations(row):
    import pandas as pd
    d = {}
    d["Operation A "] = Operation_A(row)    
    d["Operation B"] = Operation_B(row, d["Operation A "])
    d["Operation C"] = Operation_C(row)
    d["Operation D"] = Operation_D(row)
    d["Operation E"] = Operation_E(row)
    d["Operation F"] = Operation_F(row)
    d["Operation G"] = Operation_G(row, d["Operation F"], d["Operation D"], d["Operation B"])
    d["Operation H"] = Operation_H(row)
    d["Operation I"] = Operation_I(row, d["Operation H"])

    return pd.Series(d, index= ["Operation A ", "Operation B", "Operation C", "Operation D", "Operation E", "Operation F", "Operation G", "Operation H", "Operation I"])

chunk.parallel_apply(Operations)

All the Operations make string comparisons and return strings, I cannot provide an example because the functions of all these operations add to more than 400 lines of code:S

Answer 1

You can process the file as a stream without building a DataFrame . There's Table helper in convtools library ( table docs | github ). Keep in mind it reads the file as-is and doesn't infer types, it works the same as if you read the file with csv.reader yourself.

from convtools.contrib.tables import Table
from convtools import conversion as c

def Operation_A(x):
    return x == "abc"

a_values = {"1", "2"}
def Operation_B(x, y):
    return x in a_values and y

table = Table.from_csv("tmp/in.csv", header=True)

# # or if from pd.DataFrame -- unnecessary RAM usage, because Table works with
# # the stream of data
# import pandas as pd
# df = pd.DataFrame({"a": [1, 2, 3], "b": [3, 4, 5]})
# table = Table.from_rows(df.itertuples(index=False), header=list(df.columns))


table.update(
    **{
        "Operation A": c.call_func(Operation_A, c.col("b")),
        "Operation B": c.call_func(
            Operation_B, c.col("a"), c.col("Operation A")
        ),
    }
).into_csv("tmp/out.csv")
# .into_iter_rows(dict)
# .into_iter_rows(tuple, include_header=True)

I'd suggest using convtools conversions though:

(
    Table.from_csv("tmp/in.csv", header=True)
    .update(
        **{
            "Operation A": c.col("b") == "abc",
            "Operation B": c.and_(
                c.col("a").in_(c.naive(a_values)), c.col("Operation A")
            ),
        }
    )
    .into_csv("tmp/out.csv")
)