选行或列：
使用name:
`df.loc[['a','c'],['A','C']]`
使用 index:
`df.iloc[[0,1,2],[0,1,2]])`
*****
选取单个
使用name:
`df.at['c','A']`
使用index:
`df.at[1,2]`
*****
1. [DataFrame.iterrows()](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.iterrows.html)
```python
for index, row in df.iterrows():
print row["c1"], row["c2"]
```
2. [DataFrame.apply()](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.apply.html)
```
def valuation_formula(x, y):
return x * y * 0.5
df['price'] = df.apply(lambda row: valuation_formula(row['x'], row['y']), axis=1)
```
3. DataFrame.iloc()
```
for i in range(0, len(df)):
print df.iloc[i]['c1'], df.iloc[i]['c2']
```
*****
