# Can't sort a list based on a java.util.Date column?

**URL:** <https://forum.inductiveautomation.com/t/cant-sort-a-list-based-on-a-java-util-date-column/59263>\
**Category:** Ignition\
**Tags:** ignition81\
**Created:** [May 5, 2022, 6:40pm UTC](https://forum.inductiveautomation.com/t/cant-sort-a-list-based-on-a-java-util-date-column/59263 "2022-05-05T18:40:18Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![bkarabinchak.psi](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/bkarabinchak.psi/32/83567_2.png) [@bkarabinchak.psi](https://forum.inductiveautomation.com/u/bkarabinchak.psi)\
**Post date:** [May 5, 2022, 6:40pm UTC](https://forum.inductiveautomation.com/t/cant-sort-a-list-based-on-a-java-util-date-column/59263/1 "2022-05-05T18:40:18Z")

</div>

Have a duplicate rows issue in my database I am trying to correct by keeping the latest record and then making a unique constraint to stop this from happening in the future.

It’s complicated so I am doing it with jython.

I am able to get the groups of my duplicate records via query. I then want to sort them latest to oldest so I can skip the first row, and then delete all other instances.

I am working on this in my console now some sample data looks like this -

```auto
listOfRecords
[(10049, 1112, 0, None, 496), (10049, 1112, 0, Wed Sep 25 12:14:44 EDT 2019, 2292)]
>>> listOfRecords[1][3]
Wed Sep 25 12:14:44 EDT 2019
>>> type(listOfRecords[1][3])
<type 'java.util.Date'>

```

When I try to run `listOfRecords.sort(key=labmda x: x[3], reverse=True)` to sort on the timestamp column in descending order, I get a `java.lang.NullPointerException: java.lang.NullPointerException`

Using Ignition 8.1.16.

Full traceback

```auto
java.lang.NullPointerException

	at java.base/java.util.Date.getMillisOf(Unknown Source)

	at java.base/java.util.Date.compareTo(Unknown Source)

	at java.base/java.util.Date.compareTo(Unknown Source)

	at org.python.core.PyJavaType$ComparableMethod. __call__ (PyJavaType.java:1385)

	at org.python.core.PyObjectDerived. __gt__ (PyObjectDerived.java:560)

	at org.python.core.PyObject._lt(PyObject.java:1591)

	at org.python.core.PyList$KVComparator.compare(PyList.java:959)

	at org.python.core.PyList$KVComparator.compare(PyList.java:943)

	at java.base/java.util.TimSort.countRunAndMakeAscending(Unknown Source)

	at java.base/java.util.TimSort.sort(Unknown Source)

	at java.base/java.util.Arrays.sort(Unknown Source)

	at java.base/java.util.ArrayList.sort(Unknown Source)

	at java.base/java.util.Collections.sort(Unknown Source)

	at org.python.core.PyList.sort(PyList.java:998)

	at org.python.core.PyList.sort(PyList.java:790)

	at org.python.core.PyList.list_sort(PyList.java:778)

	at org.python.core.PyList$list_sort_exposer. __call__ (Unknown Source)

	at org.python.core.PyObject. __call__ (PyObject.java:400)

	at org.python.pycode._pyx165.f$0(<input>:1)

	at org.python.pycode._pyx165.call_function(<input>)

	at org.python.core.PyTableCode.call(PyTableCode.java:173)

	at org.python.core.PyCode.call(PyCode.java:18)

	at org.python.core.Py.runCode(Py.java:1687)

	at org.python.core.Py.exec(Py.java:1731)

	at org.python.util.PythonInterpreter.exec(PythonInterpreter.java:277)

	at org.python.util.InteractiveInterpreter.runcode(InteractiveInterpreter.java:130)

	at com.inductiveautomation.ignition.designer.gui.tools.jythonconsole.JythonConsole$ConsoleWorker.doInBackground(JythonConsole.java:611)

	at com.inductiveautomation.ignition.designer.gui.tools.jythonconsole.JythonConsole$ConsoleWorker.doInBackground(JythonConsole.java:599)

	at java.desktop/javax.swing.SwingWorker$1.call(Unknown Source)

	at java.base/java.util.concurrent.FutureTask.run(Unknown Source)

	at java.desktop/javax.swing.SwingWorker.run(Unknown Source)

	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

	at java.base/java.lang.Thread.run(Unknown Source)

java.lang.NullPointerException: java.lang.NullPointerException

	at org.python.core.Py.JavaError(Py.java:547)

	at org.python.core.PyTableCode.call(PyTableCode.java:182)

	at org.python.core.PyCode.call(PyCode.java:18)

	at org.python.core.Py.runCode(Py.java:1687)

	at org.python.core.Py.exec(Py.java:1731)

	at org.python.util.PythonInterpreter.exec(PythonInterpreter.java:277)

	at org.python.util.InteractiveInterpreter.runcode(InteractiveInterpreter.java:130)

	at com.inductiveautomation.ignition.designer.gui.tools.jythonconsole.JythonConsole$ConsoleWorker.doInBackground(JythonConsole.java:611)

	at com.inductiveautomation.ignition.designer.gui.tools.jythonconsole.JythonConsole$ConsoleWorker.doInBackground(JythonConsole.java:599)

	at java.desktop/javax.swing.SwingWorker$1.call(Unknown Source)

	at java.base/java.util.concurrent.FutureTask.run(Unknown Source)

	at java.desktop/javax.swing.SwingWorker.run(Unknown Source)

	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

	at java.base/java.lang.Thread.run(Unknown Source)

Caused by: java.lang.NullPointerException

	at java.base/java.util.Date.getMillisOf(Unknown Source)

	at java.base/java.util.Date.compareTo(Unknown Source)

	at java.base/java.util.Date.compareTo(Unknown Source)

	at org.python.core.PyJavaType$ComparableMethod. __call__ (PyJavaType.java:1385)

	at org.python.core.PyObjectDerived. __gt__ (PyObjectDerived.java:560)

	at org.python.core.PyObject._lt(PyObject.java:1591)

	at org.python.core.PyList$KVComparator.compare(PyList.java:959)

	at org.python.core.PyList$KVComparator.compare(PyList.java:943)

	at java.base/java.util.TimSort.countRunAndMakeAscending(Unknown Source)

	at java.base/java.util.TimSort.sort(Unknown Source)

	at java.base/java.util.Arrays.sort(Unknown Source)

	at java.base/java.util.ArrayList.sort(Unknown Source)

	at java.base/java.util.Collections.sort(Unknown Source)

	at org.python.core.PyList.sort(PyList.java:998)

	at org.python.core.PyList.sort(PyList.java:790)

	at org.python.core.PyList.list_sort(PyList.java:778)

	at org.python.core.PyList$list_sort_exposer. __call__ (Unknown Source)

	at org.python.core.PyObject. __call__ (PyObject.java:400)

	at org.python.pycode._pyx165.f$0(<input>:1)

	at org.python.pycode._pyx165.call_function(<input>)

	at org.python.core.PyTableCode.call(PyTableCode.java:173)

	... 13 more

Traceback (most recent call last):
  File "<input>", line 1, in <module>
java.lang.NullPointerException

	at java.base/java.util.Date.getMillisOf(Unknown Source)

	at java.base/java.util.Date.compareTo(Unknown Source)

	at java.base/java.util.Date.compareTo(Unknown Source)

	at org.python.core.PyJavaType$ComparableMethod. __call__ (PyJavaType.java:1385)

	at org.python.core.PyObjectDerived. __gt__ (PyObjectDerived.java:560)

	at org.python.core.PyObject._lt(PyObject.java:1591)

	at org.python.core.PyList$KVComparator.compare(PyList.java:959)

	at org.python.core.PyList$KVComparator.compare(PyList.java:943)

	at java.base/java.util.TimSort.countRunAndMakeAscending(Unknown Source)

	at java.base/java.util.TimSort.sort(Unknown Source)

	at java.base/java.util.Arrays.sort(Unknown Source)

	at java.base/java.util.ArrayList.sort(Unknown Source)

	at java.base/java.util.Collections.sort(Unknown Source)

	at org.python.core.PyList.sort(PyList.java:998)

	at org.python.core.PyList.sort(PyList.java:790)

	at org.python.core.PyList.list_sort(PyList.java:778)

	at org.python.core.PyList$list_sort_exposer. __call__ (Unknown Source)

	at org.python.core.PyObject. __call__ (PyObject.java:400)

	at org.python.pycode._pyx165.f$0(<input>:1)

	at org.python.pycode._pyx165.call_function(<input>)

	at org.python.core.PyTableCode.call(PyTableCode.java:173)

	at org.python.core.PyCode.call(PyCode.java:18)

	at org.python.core.Py.runCode(Py.java:1687)

	at org.python.core.Py.exec(Py.java:1731)

	at org.python.util.PythonInterpreter.exec(PythonInterpreter.java:277)

	at org.python.util.InteractiveInterpreter.runcode(InteractiveInterpreter.java:130)

	at com.inductiveautomation.ignition.designer.gui.tools.jythonconsole.JythonConsole$ConsoleWorker.doInBackground(JythonConsole.java:611)

	at com.inductiveautomation.ignition.designer.gui.tools.jythonconsole.JythonConsole$ConsoleWorker.doInBackground(JythonConsole.java:599)

	at java.desktop/javax.swing.SwingWorker$1.call(Unknown Source)

	at java.base/java.util.concurrent.FutureTask.run(Unknown Source)

	at java.desktop/javax.swing.SwingWorker.run(Unknown Source)

	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

	at java.base/java.lang.Thread.run(Unknown Source)

java.lang.NullPointerException: java.lang.NullPointerException

```

Tagging @JordanCClark - I know you’re handy with a dataset.

Any clue whats going wrong? I suspect the fact I have None (NULLs in my db) might be causing an issue. Not sure how to get around this.

---

<div class="post-metadata">

**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\
**Post date:** [May 5, 2022, 6:45pm UTC](https://forum.inductiveautomation.com/t/cant-sort-a-list-based-on-a-java-util-date-column/59263/2 "2022-05-05T18:45:03Z")

</div>

> [@bkarabinchak.psi](#):
>
> I suspect the fact I have None (NULLs in my db) might be causing an issue

Yeah, that's definitely the case. You could coalesce in your lambda, e.g.  
`listOfRecords.sort(key=lambda x: x[3] or False, reverse=True)` - I think that would work and put your nulls at the end.

---

<div class="post-metadata">

**Author:** ![bkarabinchak.psi](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/bkarabinchak.psi/32/83567_2.png) [@bkarabinchak.psi](https://forum.inductiveautomation.com/u/bkarabinchak.psi)\
**Post date:** [May 5, 2022, 6:47pm UTC](https://forum.inductiveautomation.com/t/cant-sort-a-list-based-on-a-java-util-date-column/59263/3 "2022-05-05T18:47:35Z")

</div>

That did the trick, thanks!

I do find it a bit odd/funny that it complains about comparing a date to a None, but knows how to compare a date to a boolean lol. Suppose there’s some conversion going on in the background or something. Anyways, thanks again!

---

<div class="post-metadata">

**Author:** ![paul-griffith](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/paul-griffith/32/37249_2.png) [@paul-griffith](https://forum.inductiveautomation.com/u/paul-griffith)\
**Post date:** [May 5, 2022, 7:40pm UTC](https://forum.inductiveautomation.com/t/cant-sort-a-list-based-on-a-java-util-date-column/59263/4 "2022-05-05T19:40:22Z")

</div>

> [@bkarabinchak.psi](#):
>
> Suppose there’s some conversion going on in the background or something.

Yeah, basically Jython is "smart" enough to see that Date implements `Comparable<Date>`, so it tries to use that logic, but Date's `compareTo` implementation is _not_ null safe. Normally sorting a list including nulls with Python is totally fine, it's just an odd edge case here.