numpy replace groups of elements with integers incrementally

Question

``` import numpy as np data = np.array(['b','b','b','a','a','a','a','c','c','d','d','d']) ``` I need to replace each group of strings with an integer incrementally like this ``` data = np.array([0,0,0,1,1,1,1,2,2,3,3,3]) ``` I'm looking for a numpy solution With this dataset http://www.uploadmb.com/dw.php?id=1364341573 ``` import numpy as np f = open('test.txt','r') lines = np.array([ line.strip() for line in f.readlines() ]) lines100 = lines[0:100] _, ind, inv = np.unique(lines100, return_index=True, return_inverse=True) print ind print inv nums = np.argsort(ind)[inv] print nums [ 0 83 62 40 19] [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1] [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4…

Accepted Answer

EDIT: This doesn't always work:

```
>>> a,b,c = np.unique(data, return_index=True, return_inverse=True)
>>> c # almost!!!
array([1, 1, 1, 0, 0, 0, 0, 2, 2, 3, 3, 3])
>>> np.argsort(b)[c]
array([0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 3], dtype=int64)
```

But this does work:

```
def replace_groups(data):
    a,b,c, = np.unique(data, True, True)
    _, ret = np.unique(b[c], False, True)
    return ret
```

and is faster than the dictionary replacement approach, about 33% for larger datasets:

```
def replace_groups_dict(data):
    _, ind = np.unique(data, return_index=True)
    unqs = data[np.sort(ind)]
    data_id = dict(zip(unqs, np.arange(data.size)))
    num = np.array([data_id[datum] for datum in data])
    return num

In [7]: %timeit replace_groups_dict(lines100)
10000 loops, best of 3: 68.8 us per loop

In [8]: %timeit replace_groups_dict(lines200)
10000 loops, best of 3: 106 us per loop

In [9]: %timeit replace_groups_dict(lines)
10 loops, best of 3: 32.1 ms per loop

In [10]: %timeit replace_groups(lines100)
10000 loops, best of 3: 67.1 us per loop

In [11]: %timeit replace_groups(lines200)
10000 loops, best of 3: 78.4 us per loop

In [12]: %timeit replace_groups(lines)
10 loops, best of 3: 23.1 ms per loop
```

numpy replace groups of elements with integers incrementally

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