Accessing property array containing string

graph-tool
1

I can't figure out how I am doing this wrong:

from graph_tool.all import *
graph = collection.data['polbooks']
a = graph.vp['value']
print a
a.get_2d_array([0])

I get this trace:
```
<PropertyMap object with key type 'Vertex' and value type 'string',
for Graph 0x7fd6f9440f90, at 0x7fd6f37322d0>

2

You cannot get a 2D array from a string property map. The value type
must be a "vector<...>".

Best,
Taigo