Create new dataframe column based on values in multiple columns

Question

FYI, performance/speed is not important for this question.

I have an existing pandas dataframe named cost_table ...

+----------+---------+------+-------------------------+-----------------+
| material | percent | qty  | price_control_indicator | acct_assign_cat |
+----------+---------+------+-------------------------+-----------------+
| abc111   | 1.00    |   50 | v                       | #               |
| abc222   | 0.25    | 2000 | s                       | #               |
| xyz789   | 0.45    |    0 | v                       | m               |
| def456   | 0.9     |    0 | v                       | #               |
| 123xyz   | 0.2     |    0 | v                       | m               |
| lmo888   | 0.6     |    0 | v                       | m               |
+----------+---------+------+-------------------------+-----------------+

I need to add a field cost_source based on values in multiple fields.

Most answers that come up on google involve a list comprehension or a ternary operator but those only include logic based on a value in one column. For example,

cost_table['cost_source'] = ['map' if qty > 0 else None for qty in cost_table['qty']]

This works based on a value in one column, but I don't know how to expand this to include logic in multiple columns (or if it's even possible?). It also doesn't seem like a very readable/maintainable solution.

I tried using a for in loop with an if elif statement but the value in cost_table['cost_source'] remains unchanged and is None for all rows. But if I print each individual row within my loop then row['cost_source'] has the desired value.

d = {
  'material': ['abc111', 'abc222', 'xyz789', 'def456', '123xyz', 'lmo888'],
  'percent': [1, .25, .45, .9, .2, .6],
  'qty': [50, 2000, 0, 0, 0, 0],
  'price_control_indicator': ['v', 's','v', 'v', 'v', 'v'],
  'acct_assign_cat': ['#', '#', 'm', '#', 'm', 'm']
}

cost_table = pd.DataFrame(data=d)

cost_table['cost_source'] = None

for index, row in cost_table.iterrows():
  if (row['qty'] > 0) or (row['price_control_indicator'] == "s") or (row['acct_assign_cat'] == "#"):
    row['cost_source'] = "map"
  elif (row['percent'] >= 40) and (row['acct_assign_cat'] == "m"):
    row['cost_source'] = "vendor"
  else:
    row['cost_source'] = None

  print(row['cost_source']) # outputs map, vendor, or None as expected

print(cost_table)

Which outputs ...

+----------+---------+------+-------------------------+-----------------+-------------+
| material | percent | qty  | price_control_indicator | acct_assign_cat | cost_source |
+----------+---------+------+-------------------------+-----------------+-------------+
| abc111   | 1.00    |   50 | v                       | #               | None        |
| abc222   | 0.25    | 2000 | s                       | #               | None        |
| xyz789   | 0.45    |    0 | v                       | m               | None        |
| def456   | 0.9     |    0 | v                       | #               | None        |
| 123xyz   | 0.2     |    0 | v                       | m               | None        |
| lmo888   | 0.6     |    0 | v                       | m               | None        |
+----------+---------+------+-------------------------+-----------------+-------------+

And this is my desired result ...

+----------+---------+------+-------------------------+-----------------+-------------+
| material | percent | qty  | price_control_indicator | acct_assign_cat | cost_source |
+----------+---------+------+-------------------------+-----------------+-------------+
| abc111   | 1.00    |   50 | v                       | #               | map         |
| abc222   | 0.25    | 2000 | s                       | #               | map         |
| xyz789   | 0.45    |    0 | v                       | m               | vendor      |
| def456   | 0.9     |    0 | v                       | #               | map         |
| 123xyz   | 0.2     |    0 | v                       | m               | None        |
| lmo888   | 0.6     |    0 | v                       | m               | vendor      |
+----------+---------+------+-------------------------+-----------------+-------------+

Answer 1

If you wish to use np.select

cond1 = cost_table.qty.gt(0) | cost_table.price_control_indicator.eq('s') | cost_table.acct_assign_cat.eq('#')
cond2 = cost_table.percent.ge(0.4) & cost_table.acct_assign_cat.eq('m')
cost_table['cost_source'] = np.select([cond1, cond2], ['map', 'vendor'], default='None')
print(cost_table)

  material  percent   qty price_control_indicator acct_assign_cat cost_source
0   abc111     1.00    50                       v               #         map
1   abc222     0.25  2000                       s               #         map
2   xyz789     0.45     0                       v               m      vendor
3   def456     0.90     0                       v               #         map
4   123xyz     0.20     0                       v               m        None
5   lmo888     0.60     0                       v               m      vendor

Answer 2

As @bazinga stated, use df.apply(lambda x: fun(x), but with parameter axis=1, so the lambda function is applied to row by row (default is column by column).

d = {
  'material': ['abc111', 'abc222', 'xyz789', 'def456', '123xyz', 'lmo888'],
  'percent': [100, 25, 45, 90, 20, 60],
  'qty': [50, 2000, 0, 0, 0, 0],
  'price_control_indicator': ['v', 's','v', 'v', 'v', 'v'],
  'acct_assign_cat': ['#', '#', 'm', '#', 'm', 'm']
}

cost_table = pd.DataFrame(data=d)

def process_row(row):
    if (row['qty'] > 0) or (row['price_control_indicator'] == "s") or (row['acct_assign_cat'] == "#"):
        return "map"
    elif (row['percent'] >= 40) and (row['acct_assign_cat'] == "m"):
        return "vendor"
    else:
        return None

cost_table['cost_source'] = cost_table.apply(lambda row: process_row(row), axis=1)

print(cost_table)

(I also corrected an inconsistency: in the data procents should be probably multiplied by 100)