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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?










0















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.



first two maximum values



maximun










share|improve this question



















  • 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















0















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.



first two maximum values



maximun










share|improve this question



















  • 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













0












0








0


1






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.



first two maximum values



maximun










share|improve this question
















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.



first two maximum values



maximun







qgis pyqgis qgis-3 qgis-processing






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited yesterday









Vince

14.8k32849




14.8k32849










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












  • 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










1 Answer
1






active

oldest

votes


















3














This expression will give you the second-largest value:



array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))


It works by



  1. put all the "fieldname" values into an array (ie, a list)

  2. remove all instances of the maximum value from the array

  3. sort the array from smallest to largest

  4. 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.






share|improve this answer























  • 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











Your Answer








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1 Answer
1






active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









3














This expression will give you the second-largest value:



array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))


It works by



  1. put all the "fieldname" values into an array (ie, a list)

  2. remove all instances of the maximum value from the array

  3. sort the array from smallest to largest

  4. 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.






share|improve this answer























  • 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















3














This expression will give you the second-largest value:



array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))


It works by



  1. put all the "fieldname" values into an array (ie, a list)

  2. remove all instances of the maximum value from the array

  3. sort the array from smallest to largest

  4. 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.






share|improve this answer























  • 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













3












3








3







This expression will give you the second-largest value:



array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))


It works by



  1. put all the "fieldname" values into an array (ie, a list)

  2. remove all instances of the maximum value from the array

  3. sort the array from smallest to largest

  4. 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.






share|improve this answer













This expression will give you the second-largest value:



array_last(array_sort(array_remove_all( array_agg( "fieldname"), maximum("fieldname"))))


It works by



  1. put all the "fieldname" values into an array (ie, a list)

  2. remove all instances of the maximum value from the array

  3. sort the array from smallest to largest

  4. 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.







share|improve this answer












share|improve this answer



share|improve this answer










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

















  • 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

















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