Using QGIS 1.8, I've got a shapefile with an integer field called "AREA" and I'd like to sum the values which are in this shapefile.
Does anybody know how to?
[GIS] Summing values in field
fields-attributesqgis-2summarizing
Related Solutions
It is simpler than with version 1.8:
layer = qgis.utils.iface.activeLayer()
fields = layer.pendingFields()
field_names = [field.name() for field in fields]
or in one line
field_names = [field.name() for field in layer.pendingFields() ]
an after
for elem in layer.getFeatures():
print dict(zip(field_names, elem.attributes()))
{u'adip': 17, u'dipdir': 130, u'tdip': 29}
{u'adip': 55, u'dipdir': 325, u'tdip': 75}
.....
Generally to explore a new function, I use the dir() or the see module to examine what's inside:
dir(fields)
['FieldOrigin', 'OriginEdit', 'OriginJoin', 'OriginProvider', 'OriginUnknown', '__class__', '__delattr__', '__delitem__', '__dict__', '__doc__', '__format__', '__getattribute__', '__getitem__', '__hash__', '__init__', '__len__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'append', 'at', 'clear', 'count', 'extend', 'field', 'fieldOrigin', 'fieldOriginIndex', 'indexFromName', 'isEmpty', 'remove', 'size', 'toList']
or
see(fields)
[] hash() help() len()
repr() str() .FieldOrigin() .OriginEdit
.OriginJoin .OriginProvider .OriginUnknown .append()
.at() .clear() .count() .extend()
.field() .fieldOrigin() .fieldOriginIndex()
.indexFromName() .isEmpty() .remove() .size()
.toList()
And you can see that there is a field() function so
print fields.field(0)
qgis.core.QgsField object at 0x163E39C0
and a field has a name, a type, a precision,...:
see(fields.field(0))
< <= == != >
>= hash() help() repr()
str() .comment() .displayString() .length()
.name() .precision() .setComment() .setLength()
.setName() .setPrecision() .setType() .setTypeName()
.type() .typeName()
so:
fields.field(0).name()
u'adip'
fields.field(0).type()
2
fields.field(0).typeName()
u'Integer'
fields.field(0).precision()
0
....
with .dataProvider()
It is .field()
....
prov = layer.dataProvider()
prov.fields().field(0).name()
u'adip'
prov.fields().field(0).typeName()
u'Integer'
and
field_names = [field.name() for field in prov.fields()]
This can be achieved with a relatively simple model, no programming required! The model is below:
I use the summary statistics tool to sum your first field and place this value in an in_memory table. Then use the get Field value tool (a model only tool) to get that value. Then a simple calculate field tool on your second field using in-line substitution (in this case %SUM value%). The output of the Get Field value tool is a precondition to the calculate field tool so it runs in the correct order.
Best Answer
You can immediately get field summary data, including sums, from the menu Vector|Analysis tools|Basic statistics:
You could also open the .dbf file associated with your shapefile in Excel or OpenOffice, and you'll be able to work with all the field values as a spreadsheet.