# Converting table headers to PyDataSet **URL:** \ **Category:** Ignition\ **Created:** [July 2, 2019, 5:18pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234 "2019-07-02T17:18:28Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Peter.Dmitriev](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@Peter.Dmitriev](https://forum.inductiveautomation.com/u/Peter.Dmitriev)\ **Post date:** [July 2, 2019, 5:18pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/1 "2019-07-02T17:18:28Z")
Hello, I have a simple task of writing table column names to PLC tags but it doesn’t want to convert the list to PyDataSet. Here is the code: headerVals = event.source.parent.getComponent(‘Power Table’).data.getColumnNames() headersToPLC = system.dataset.toPyDataSet(headerVals) Here is the error message: TypeError: toPyDataSet(): 1st arg can’t be coerced to com.inductiveautomation.ignition.common.Dataset It seems like I need to convert **java.util.Collections$UnmodifiableRandomAccessList** (that’s what _print type(headerVals)_ gives me) to Ignition dataset but I couldn’t figure out how to do it. Any suggestions? Thanks, Peter. ---
**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:** [July 2, 2019, 5:28pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/2 "2019-07-02T17:28:42Z")
PyDatasets are (basically) **2D** arrays, AKA lists _of lists_; the datastructure in pure Python would be something like: ```python pds = [ [col1, col2, col3], # row1 [col1, col2, col3], # row2 [col1, col2, col3], # row3 ] ``` `getColumnNames()` returns a flat list: `[columnName1, columnName2, columnName2]` Why are you trying to cast it into a pydataset? What’s the desired operation? You _may_ just need to put it inside of another list, but that’s skipping the actual question: ```python headerVals = event.source.parent.getComponent(‘Power Table’).data.getColumnNames() headersToPLC = system.dataset.toPyDataSet([headerVals]) ``` ---
**Author:** ![Peter.Dmitriev](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@Peter.Dmitriev](https://forum.inductiveautomation.com/u/Peter.Dmitriev)\ **Post date:** [July 2, 2019, 5:44pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/3 "2019-07-02T17:44:23Z")
@paul-griffith, All I need is to write this data to PLC tags. I want to use system.opc.writeValues(). I’ve tried putting header list inside of another list with no luck - gives me the same error. Does it work for you? I’m running 7.9.10. ---
**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:** [July 2, 2019, 5:57pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/4 "2019-07-02T17:57:23Z")
`system.opc.writeValues` expects a flat list of paths and values - something like: ```auto paths = ["path1", "path2", "path3"] values = event.source.parent.getComponent(‘Power Table’).data.getColumnNames() system.opc.writeValues("Ignition OPC UA Server", paths, values) ``` No PyDatasets required - I’m not sure why you started down that path. Are you able to share a bit more of your script so I can see more of what you’re trying to do? ---
**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:** [July 2, 2019, 5:58pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/5 "2019-07-02T17:58:56Z")
Or (pure speculation) are you trying to use the table headers to determine _which_ OPC tags to write to? And then extract values from somewhere else (the table data?) If so, this gets a bit more complicated, but still shouldn’t necessarily require PyDatasets. ---
**Author:** ![Peter.Dmitriev](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@Peter.Dmitriev](https://forum.inductiveautomation.com/u/Peter.Dmitriev)\ **Post date:** [July 2, 2019, 6:13pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/6 "2019-07-02T18:13:39Z")
Yes, that’s exactly where I started but it didn’t work for me: ```auto basePath = 'ns=1;s=[' + event.source.parent.getComponent('PAC').text + ']' + event.source.parent.getComponent('TagName').text opcuaServer = event.source.parent.getComponent('OPCUA').text headerPaths = [] headerPaths.append(basePath + '.Headers[0]') headerPaths.append(basePath + '.Headers[1]') headerPaths.append(basePath + '.Headers[2]') headerPaths.append(basePath + '.Headers[3]') headerPaths.append(basePath + '.Headers[4]') headerVals = event.source.parent.getComponent('Power Table').data.getColumnNames() system.opc.writeValues(opcuaServer,headerPaths,headerVals) ``` Error: java.lang.ClassCastException: java.lang.ClassCastException: Cannot coerce value ‘[Meter Pressure, Meter K-factor, Meter F/V, Meter Frequency, Meter Density]’ into type: class [Ljava.lang.Object; Now, here is part of the code that writes the actual table data to PLC tags. I could only make it work with Py datasets. System.opc.writeValues operates only on single row PyDataSets from what i can see: ```auto intData = system.dataset.toPyDataSet(event.source.parent.getComponent('Power Table').data) intPath = basePath + '.INT' i=0 for i in range(0,20): intRowPaths = [] intRowVals = [] for k in range(0,5): intRowPaths.append(intPath + str(k+1) + '[' + str(i)+ ']') intRowVals.append(intData[i][k]) system.opc.writeValues(opcuaServer,intRowPaths,intRowVals) ``` What am I missing something here? Thanks for the help @paul-griffith ---
**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:** [July 2, 2019, 6:18pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/7 "2019-07-02T18:18:06Z")
Try updating the first example to this: ```auto basePath = 'ns=1;s=[' + event.source.parent.getComponent('PAC').text + ']' + event.source.parent.getComponent('TagName').text opcuaServer = event.source.parent.getComponent('OPCUA').text headerPaths = [] headerPaths.append(basePath + '.Headers[0]') headerPaths.append(basePath + '.Headers[1]') headerPaths.append(basePath + '.Headers[2]') headerPaths.append(basePath + '.Headers[3]') headerPaths.append(basePath + '.Headers[4]') headerVals = list(event.source.parent.getComponent('Power Table').data.getColumnNames()) system.opc.writeValues(opcuaServer,headerPaths,headerVals) ``` ---
**Author:** ![Peter.Dmitriev](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@Peter.Dmitriev](https://forum.inductiveautomation.com/u/Peter.Dmitriev)\ **Post date:** [July 2, 2019, 6:48pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/8 "2019-07-02T18:48:03Z")
That did the trick, Paul @paul-griffith Thanks for your help! ---
**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:** [July 2, 2019, 7:25pm UTC](https://forum.inductiveautomation.com/t/converting-table-headers-to-pydataset/26234/9 "2019-07-02T19:25:15Z")
For a little background - it looks like the `java.util.Collections$UnmodifiableRandomAccessList` that is returned from `getColumnNames` isn’t a close enough type to a regular Python list to be coerced by system.opc.writeValues - so, calling the `list()` function automatically creates a new, true `list` class instance based on the sequence of values provided - the `UnmodifiableRandomAccessList`.