Apply a function with arguments to each row using df.apply()

Question

I've seen enough SO questions about using pandas df.apply() function when the function being applied is super trivial (like .upper(), or simple multiplication). However, when I try to apply my custom function, I keep getting all sorts of errors. I don't know where to start with this error:

Here is my simplified example:

My fake data:

inp = [{'c1':10, 'c2':1}, {'c1':11,'c2':110}, {'c1':12,'c2':0}]
df1 = pd.DataFrame(inp)
print(df1)

My fake function

def fake_funk(row, upper, lower):
    if lower < row['c1'] < upper:
        return(1)
    elif row['c2'] > upper:
        return(2)
    else:
        return(0)

Testing that it does in fact work:

for index, row in df1.iterrows():
    print(fake_funk(row,11,1))
1
2
0

Now using apply()

df1.apply(lambda row,: fake_funk(row,11,1))

The error I am getting is pretty long:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc (pandas/_libs/index.c:5126)()

pandas/_libs/hashtable_class_helper.pxi in pandas._libs.hashtable.Int64HashTable.get_item (pandas/_libs/hashtable.c:14010)()

TypeError: an integer is required

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
<ipython-input-116-a554e891e761> in <module>()
----> 1 df1.apply(lambda row,: fake_funk(row,11,1))

/usr/local/anaconda3/lib/python3.5/site-packages/pandas/core/frame.py in apply(self, func, axis, broadcast, raw, reduce, args, **kwds)
   4260                         f, axis,
   4261                         reduce=reduce,
-> 4262                         ignore_failures=ignore_failures)
   4263             else:
   4264                 return self._apply_broadcast(f, axis)

/usr/local/anaconda3/lib/python3.5/site-packages/pandas/core/frame.py in _apply_standard(self, func, axis, ignore_failures, reduce)
   4356             try:
   4357                 for i, v in enumerate(series_gen):
-> 4358                     results[i] = func(v)
   4359                     keys.append(v.name)
   4360             except Exception as e:

<ipython-input-116-a554e891e761> in <lambda>(row)
----> 1 df1.apply(lambda row,: fake_funk(row,11,1))

<ipython-input-115-e95f3470fb25> in fake_funk(row, upper, lower)
      1 def fake_funk(row, upper, lower):
----> 2     if lower < row['c1'] < upper:
      3         return(1)
      4     elif row['c2'] > upper:
      5         return(2)

/usr/local/anaconda3/lib/python3.5/site-packages/pandas/core/series.py in __getitem__(self, key)
    599         key = com._apply_if_callable(key, self)
    600         try:
--> 601             result = self.index.get_value(self, key)
    602 
    603             if not is_scalar(result):

/usr/local/anaconda3/lib/python3.5/site-packages/pandas/core/indexes/base.py in get_value(self, series, key)
   2475         try:
   2476             return self._engine.get_value(s, k,
-> 2477                                           tz=getattr(series.dtype, 'tz', None))
   2478         except KeyError as e1:
   2479             if len(self) > 0 and self.inferred_type in ['integer', 'boolean']:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_value (pandas/_libs/index.c:4404)()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_value (pandas/_libs/index.c:4087)()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc (pandas/_libs/index.c:5210)()

KeyError: ('c1', 'occurred at index c1')

Answer 1

By default, apply operates along the 0th axis. It seems you need an operation along the 1st axis. By the way, you don't need a lambda either. Just pass an args parameter, which should be enough.

df1.apply(fake_funk, axis=1, args=(11, 1))

0    1
1    2
2    0
dtype: int64