Nearest neighbor analysis not showing results

Question

I'm trying to do a nearest neighbour analysis on fish shoals distribution. I go to Vector > Analysis Tools > Nearest neighbour analysis. I choose the appropriate layer and when I hit ok the black and white wheel is on, and nothing happens; I think it IS doing the analysis because the blue bar is 100%; but just not showing anything.

Has anyone had this problem and know how to solve it?

I'm using: QGIS 1.8.0-Lisboa GDAL 1.9.1 With Mac OS X 10.7.5

Answer 1

This a Python solution (comes installed with QGIS):

Make sure to have shapely installed.

Here's the Python script, neighbors.py and run this script in the Python Console (Plugins -> Python Console):

from PyQt4.QtCore import *
from shapely.wkb import loads

# Replace the below value with the field containing name or id of the feature
# For example, if your field is called name then change the line below to
# name_field = 'name'
name_field = 'NAME'

# Replace the below value with the field name that you want to sum up
sum_field = 'POP_EST'

layer = qgis.utils.iface.activeLayer()
layer.startEditing()
provider = layer.dataProvider()

# We add 2 attributes to the current layer
provider.addAttributes( [QgsField("Neighbors", QVariant.String),
                    QgsField("Sum", QVariant.Int)])
neighbor_name_index = provider.fieldNameIndex("Neighbors")
neighbor_sum_index = provider.fieldNameIndex("Sum")
allAttrs = provider.attributeIndexes()

# Select all features along with their attributes
provider.select(allAttrs)
feat = QgsFeature()
polygon_dict = {}

# Loop through all features and store their geometry and relevant attributes in
# a dictionary
while provider.nextFeature(feat):
feature_id = feat.id()
attrmap = feat.attributeMap()
name = attrmap[provider.fieldNameIndex(name_field)].toString()
sum_value = attrmap[provider.fieldNameIndex(sum_field)].toInt()[0]
print 'Reading Geometry for %s' % name
geom = feat.geometry()
wkb = geom.asWkb()
polygon = loads(wkb)
polygon_dict[feature_id] = [ polygon, name, sum_value ]

# Now one-by-one take a feature and find all other features that touch its
# geometry
all_polygons = polygon_dict.keys()
attribute_dict = {}

for polygon_id in all_polygons:
this_polygon, this_name, this_sum = polygon_dict[polygon_id]
neighbor_list = []
sum_of_neighbors = 0

for polygon_id_compare in all_polygons:
compare_polygon, compare_name, compare_sum = polygon_dict[polygon_id_compare]
if this_polygon.touches(compare_polygon):
neighbor_list.append(unicode(compare_name))
sum_of_neighbors += compare_sum

# Make a list of all neighbors' names
neighbor_string = ','.join(neighbor_list)
attribute_dict[polygon_id] = {neighbor_name_index: QVariant(neighbor_string),
                           neighbor_sum_index: QVariant(sum_of_neighbors)}

# Update the attribute table
provider.changeAttributeValues(attribute_dict)
layer.commitChanges()
layer.stopEditing()

Try using this suggestion and this tutorial.

Vector -> Analysis -> Distance Matrix