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How to obtain the maximum two values of a field, without having to do it manually in the attribute table?
The Next CEO of Stack OverflowVia PyQgis how to refresh a modified CSV layer without having to reopen the file?Finding Median, Max and Min values from Raster Layers in QGISHow to get attribute values from vector features visible in the qgis canvasUpdate/change/commit an attribute/a field value “on the fly” in QGIS 3What geodetic reference system is QGIS using when providing latitude and longitude values for points using the field calculator?QGIS Attribute table - How to merge the values of $area field of several elements by the same attribute (point ID)?Getting maximum values of attribute of multiple Shapefiles merged into new shapefile in QGIS?Unexpected behaviour using Filter in QGIS 3.2QGIS RASTER CALCULATOR - Getting the Minimum and Maximum Values of a Raster LayerHow to display an attribute value from a related layer in Atlas?
I have a layer of points corresponding to the vertices extracted from a polygon, and from these I need to obtain the two maximum values and save them in a new layer of points.
Because I have more than 150 layers of points I would like to know if it is possible to do it without having to open the table of attributes of each of these and select the values that interest me.
I tried using the field calculator using the expression "maximum(expression[,group_by][,filter])" but that would not have the second maximum.
qgis pyqgis qgis-3 qgis-processing
edited yesterday
Vince
14.8k32849
asked yesterday
JohnJohn
254
add a comment |
I have a layer of points corresponding to the vertices extracted from a polygon, and from these I need to obtain the two maximum values and save them in a new layer of points.
Because I have more than 150 layers of points I would like to know if it is possible to do it without having to open the table of attributes of each of these and select the values that interest me.
I tried using the field calculator using the expression "maximum(expression[,group_by][,filter])" but that would not have the second maximum.
qgis pyqgis qgis-3 qgis-processing
edited yesterday
Vince
14.8k32849
asked yesterday
JohnJohn
254
2
Do u mean u're searching a way to achieve this programmatically for your 150 layers ? Are they opened ? Are they named using the same scheme ? Getting the two max. values is easy using a query on the table but is your question rather how to automate the whole process ?
– snaileater
yesterday
2
Of course it isn't possible to find attribute values without opening the attribute table. But this is trivially simple to script. What have you tried?
– Vince
yesterday
Yes, I understand that it is essential to access the attribute table. I already tried the field calculator with the expression "maximun" but I would need the second highest value. How could I implement a query for this value?
– John
yesterday
add a comment |
I have a layer of points corresponding to the vertices extracted from a polygon, and from these I need to obtain the two maximum values and save them in a new layer of points.
Because I have more than 150 layers of points I would like to know if it is possible to do it without having to open the table of attributes of each of these and select the values that interest me.
I tried using the field calculator using the expression "maximum(expression[,group_by][,filter])" but that would not have the second maximum.
qgis pyqgis qgis-3 qgis-processing
edited yesterday
Vince
14.8k32849
asked yesterday
JohnJohn
254
I have a layer of points corresponding to the vertices extracted from a polygon, and from these I need to obtain the two maximum values and save them in a new layer of points.
Because I have more than 150 layers of points I would like to know if it is possible to do it without having to open the table of attributes of each of these and select the values that interest me.
I tried using the field calculator using the expression "maximum(expression[,group_by][,filter])" but that would not have the second maximum.
qgis pyqgis qgis-3 qgis-processing
qgis pyqgis qgis-3 qgis-processing
edited yesterday
Vince
14.8k32849
asked yesterday
JohnJohn
254
edited yesterday
Vince
14.8k32849
asked yesterday
JohnJohn
254
edited yesterday
Vince
14.8k32849
edited yesterday
Vince
14.8k32849
edited yesterday
Vince
14.8k32849
14.8k32849
asked yesterday
JohnJohn
254
asked yesterday
JohnJohn
254
asked yesterday
JohnJohn
254
254
2
Do u mean u're searching a way to achieve this programmatically for your 150 layers ? Are they opened ? Are they named using the same scheme ? Getting the two max. values is easy using a query on the table but is your question rather how to automate the whole process ?
– snaileater
yesterday
2
Of course it isn't possible to find attribute values without opening the attribute table. But this is trivially simple to script. What have you tried?
– Vince
yesterday
Yes, I understand that it is essential to access the attribute table. I already tried the field calculator with the expression "maximun" but I would need the second highest value. How could I implement a query for this value?
– John
yesterday
add a comment |
2
Do u mean u're searching a way to achieve this programmatically for your 150 layers ? Are they opened ? Are they named using the same scheme ? Getting the two max. values is easy using a query on the table but is your question rather how to automate the whole process ?
– snaileater
yesterday
2
Of course it isn't possible to find attribute values without opening the attribute table. But this is trivially simple to script. What have you tried?
– Vince
yesterday
Yes, I understand that it is essential to access the attribute table. I already tried the field calculator with the expression "maximun" but I would need the second highest value. How could I implement a query for this value?
– John
yesterday
2
2
Do u mean u're searching a way to achieve this programmatically for your 150 layers ? Are they opened ? Are they named using the same scheme ? Getting the two max. values is easy using a query on the table but is your question rather how to automate the whole process ?
– snaileater
yesterday
Do u mean u're searching a way to achieve this programmatically for your 150 layers ? Are they opened ? Are they named using the same scheme ? Getting the two max. values is easy using a query on the table but is your question rather how to automate the whole process ?
– snaileater
yesterday
2
2
Of course it isn't possible to find attribute values without opening the attribute table. But this is trivially simple to script. What have you tried?
– Vince
yesterday
Of course it isn't possible to find attribute values without opening the attribute table. But this is trivially simple to script. What have you tried?
– Vince
yesterday
Yes, I understand that it is essential to access the attribute table. I already tried the field calculator with the expression "maximun" but I would need the second highest value. How could I implement a query for this value?
– John
yesterday
Yes, I understand that it is essential to access the attribute table. I already tried the field calculator with the expression "maximun" but I would need the second highest value. How could I implement a query for this value?
– John
yesterday
add a comment |
1 Answer
1
active
oldest
votes
This expression will give you the second-largest value:
array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))
It works by
- put all the "fieldname" values into an array (ie, a list)
- remove all instances of the maximum value from the array
- sort the array from smallest to largest
- extract the last value in the array
Note: This solution will work in QGIS 3.6 and later. The array_sort function doesn't exist in earlier versions.
answered yesterday
cskcsk
9,4751035
thanks, it works great
– John
yesterday
Happy to help. You can mark this answer as accepted by clicking the checkmark next to the answer. That way others with the same question will know that this method works.
– csk
yesterday
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
This expression will give you the second-largest value:
array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))
It works by
- put all the "fieldname" values into an array (ie, a list)
- remove all instances of the maximum value from the array
- sort the array from smallest to largest
- extract the last value in the array
Note: This solution will work in QGIS 3.6 and later. The array_sort function doesn't exist in earlier versions.
answered yesterday
cskcsk
9,4751035
thanks, it works great
– John
yesterday
Happy to help. You can mark this answer as accepted by clicking the checkmark next to the answer. That way others with the same question will know that this method works.
– csk
yesterday
add a comment |
This expression will give you the second-largest value:
array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))
It works by
- put all the "fieldname" values into an array (ie, a list)
- remove all instances of the maximum value from the array
- sort the array from smallest to largest
- extract the last value in the array
Note: This solution will work in QGIS 3.6 and later. The array_sort function doesn't exist in earlier versions.
answered yesterday
cskcsk
9,4751035
thanks, it works great
– John
yesterday
Happy to help. You can mark this answer as accepted by clicking the checkmark next to the answer. That way others with the same question will know that this method works.
– csk
yesterday
add a comment |
This expression will give you the second-largest value:
array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))
It works by
- put all the "fieldname" values into an array (ie, a list)
- remove all instances of the maximum value from the array
- sort the array from smallest to largest
- extract the last value in the array
Note: This solution will work in QGIS 3.6 and later. The array_sort function doesn't exist in earlier versions.
answered yesterday
cskcsk
9,4751035
This expression will give you the second-largest value:
array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))
It works by
- put all the "fieldname" values into an array (ie, a list)
- remove all instances of the maximum value from the array
- sort the array from smallest to largest
- extract the last value in the array
Note: This solution will work in QGIS 3.6 and later. The array_sort function doesn't exist in earlier versions.
answered yesterday
cskcsk
9,4751035
answered yesterday
cskcsk
9,4751035
answered yesterday
cskcsk
9,4751035
answered yesterday
cskcsk
9,4751035
9,4751035
thanks, it works great
– John
yesterday
Happy to help. You can mark this answer as accepted by clicking the checkmark next to the answer. That way others with the same question will know that this method works.
– csk
yesterday
add a comment |
thanks, it works great
– John
yesterday
Happy to help. You can mark this answer as accepted by clicking the checkmark next to the answer. That way others with the same question will know that this method works.
– csk
yesterday
thanks, it works great
– John
yesterday
thanks, it works great
– John
yesterday
Happy to help. You can mark this answer as accepted by clicking the checkmark next to the answer. That way others with the same question will know that this method works.
– csk
yesterday
Happy to help. You can mark this answer as accepted by clicking the checkmark next to the answer. That way others with the same question will know that this method works.
– csk
yesterday
add a comment |
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2
Do u mean u're searching a way to achieve this programmatically for your 150 layers ? Are they opened ? Are they named using the same scheme ? Getting the two max. values is easy using a query on the table but is your question rather how to automate the whole process ?
– snaileater
yesterday
2
Of course it isn't possible to find attribute values without opening the attribute table. But this is trivially simple to script. What have you tried?
– Vince
yesterday
Yes, I understand that it is essential to access the attribute table. I already tried the field calculator with the expression "maximun" but I would need the second highest value. How could I implement a query for this value?
– John
yesterday