Turn the following data concerning various species of cetacean into a NumPy structured array and order it by (a) mass and (b) population. Determine in each case the index at which Bryde's whale (population: 100000, mass: 25 tonnes) should be inserted to keep the array ordered.
| Name | Population | Mass /tonnes |
|---|---|---|
| Bowhead whale | 9000 | 60 |
| Blue whale | 20000 | 120 |
| Fin whale | 100000 | 70 |
| Humpback whale | 80000 | 30 |
| Gray whale | 26000 | 35 |
| Atlantic white-sided dolphin | 250000 | 0.235 |
| Pacific white-sided dolphin | 1000000 | 0.15 |
| Killer whale | 100000 | 4.5 |
| Narwhal | 25000 | 1.5 |
| Beluga | 100000 | 1.5 |
| Sperm whale | 2000000 | 50 |
| Baiji | 13 | 0.13 |
| North Atlantic right whale | 300 | 75 |
| North Pacific right whale | 200 | 80 |
| Southern right whale | 7000 | 70 |
A text file containing these data is available as whale-data.txt.
First define a suitable data type:
In [x]: dt = np.dtype([('Common Name', 'S32'), ('Population', 'i4'),
....: ('Mass', 'f8')])
and populate a structured array in the arbitrary order given:
In [x]: cetaceans = np.array(
....: [
....: ('Bowhead whale', 9000, 60),
....: ('Blue whale', 20000, 120),
....: ('Fin whale', 100000, 70),
....: ('Humpback whale', 80000, 30),
....: ('Gray whale', 26000, 35),
....: ('Atlantic white-sided dolphin', 250000, 0.235),
....: ('Pacific white-sided dolphin', 1000000, 0.15),
....: ('Killer whale', 100000, 4.5),
....: ('Narwhal', 25000, 1.5),
....: ('Beluga', 100000, 1.5),
....: ('Sperm whale', 2000000, 50),
....: ('Baiji', 13, 0.13),
....: ('North Atlantic right whale', 300, 75),
....: ('North Pacific right whale', 200, 80),
....: ('Southern right whale', 7000, 70)
....: ], dtype=dt)
(a) Sort by mass and find the index to insert Bryde's whale:
In [x]: cetaceans.sort(order='Mass')
In [x]: new_whale = np.array(("Bryde's whale", 100000, 25), dtype=dt)
In [x]: np.searchsorted(cetaceans['Mass'], new_whale['Mass'])
Out[x]: 6
(b) Similarly, re-order by population
In [x]: cetaceans.sort(order='Population')
In [x]: np.searchsorted(cetaceans['Population'], new_whale['Population'])
Out[x]: 9