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## [igraph] python-igraph data to numpy

 From: Andreas Geiges Subject: [igraph] python-igraph data to numpy Date: Thu, 15 Feb 2018 17:19:40 +0100 User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

```Dear Igraph users,

I am using python-igraph in python2.7 in combination with numpy.

```
I need to speed up the following scenario and was wondering if someone can give my some hints.
```I have a large graph with several thousands of vertices.
```
One property of the vertices is a one-dimensional numpy array ( e.g. array([0,0,0,0]) )
```
```
If I read out the property of one vertice, I get the numpy array directly back, no conversion needed. But if I read the property of an vertice sequence, I get a list of array, which is perfectly fine. BUT I like to have the data as a 2D-array in numpy, thus I need to use numpy.asarray() which cause an overhead, which
```cost me a lost of computing time form many of this operation.

```
Thus, I was wondering if there is a way, to directly receive a 2D-array back from igraph, when using a sequence.
```I think this is not possible right now, but maybe it can be implemented.
I would be willing to try that, but I would need some hints, where to start.

The following code is maybe demonstrating better what I want to accomplish:

######################################
import igraph  as ig
import numpy as np
from  timeit import timeit as ti
#%%  Setup
graph = ig.Graph()

nVert = 1000

for vertice in graph.vs:
vertice['property'] = np.random.random(5)
#print vertice

#creation of a arbitray sequence
vertexSequence = graph.vs[np.arange(0,nVert,5).tolist()]

#%% reading the properties of a sequence to an numpy array

#first possiblity using asarray
```
%timeit numpyArray2D = np.asarray(vertexSequence['property'],dtype=np.float64)
```
#second possiblity with pre-allocated array and numpy view
numpyArray2D = np.zeros([len(vertexSequence),5])
%timeit numpyArray2D[:] = vertexSequence['property']
######################################

Best,
Andreas

--
Dr.-Ing. Andreas Geiges

Global Climate Forum (GCF)
Neue Promenade 6, D-10178 Berlin, Germany
http://www.globalclimateforum.org

```