# How to use 'previousRawValue' and 'previousBlockResults' in a Custom Tag History Aggregate function **URL:** \ **Category:** Ignition\ **Tags:** ignition81\ **Created:** [September 7, 2022, 11:37pm UTC](https://forum.inductiveautomation.com/t/how-to-use-previousrawvalue-and-previousblockresults-in-a-custom-tag-history-aggregate-function/63863 "2022-09-07T23:37:38Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![tyler.bennett](https://avatars.discourse-cdn.com/v4/letter/t/f04885/32.png) [@tyler.bennett](https://forum.inductiveautomation.com/u/tyler.bennett)\ **Post date:** [September 7, 2022, 11:37pm UTC](https://forum.inductiveautomation.com/t/how-to-use-previousrawvalue-and-previousblockresults-in-a-custom-tag-history-aggregate-function/63863/1 "2022-09-07T23:37:38Z")
`blockContext.previousRawValue` and `blockContext.previousBlockResults` as described in the [Custom Tag History Aggregates](https://docs.inductiveautomation.com/display/DOC81/Custom+Tag+History+Aggregates) documentation are actually bound functions and must be utilized with parentheses to get the expected return value/object. Perhaps that is obvious to others but it took quite a bit of tinkering to figure that out and thought I’d share as there is very little mention of those in the forums. **Example Usage:** ``` print "blockContext.previousRawValue: {}".format(blockContext.previousRawValue) # - QualifiedValue, the previous non-interpolated value received before this window print "blockContext.previousBlockResults: {}".format(blockContext.previousBlockResults) # - QualifiedValue[], the results of the previous window. print "blockContext.previousRawValue(): {}".format(blockContext.previousRawValue()) # - QualifiedValue, the previous non-interpolated value received before this window print "blockContext.previousBlockResults(): {}".format(blockContext.previousBlockResults()) # - QualifiedValue[], the results of the previous window. ``` **Results:** ``` INFO | jvm 2 | 2022/09/07 18:14:09 | blockContext.previousRawValue: bound method com.inductiveautomation.ignition.gateway.sqltags.history.query.processing.BlockContext.previousRawValue of {u'count': 1} INFO | jvm 2 | 2022/09/07 18:14:09 | blockContext.previousBlockResults: bound method com.inductiveautomation.ignition.gateway.sqltags.history.query.processing.BlockContext.previousBlockResults of {u'count': 1} INFO | jvm 2 | 2022/09/07 18:14:09 | blockContext.previousRawValue(): {v=43.54100036621094, q=Good, ts=Wed Sep 07 18:14:01 CDT 2022, intrp=false} INFO | jvm 2 | 2022/09/07 18:14:09 | blockContext.previousBlockResults(): array(com.inductiveautomation.ignition.common.model.values.QualifiedValue, [[-88, Good, Wed Sep 07 18:04:08 CDT 2022 (1662591848114)]]) ``` @Colby.Clegg This is/was not clear in the documentation (to me), I suggest updating the documentation text and examples. I directed that comment at you solely because you provided the [earliest reference to the documentation](https://forum.inductiveautomation.com/t/valid-data-point-calculation-from-sql/11090/2) that I could find in the forums. Thanks. Ignition v8.1.19 ---
**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:** [September 7, 2022, 11:41pm UTC](https://forum.inductiveautomation.com/t/how-to-use-previousrawvalue-and-previousblockresults-in-a-custom-tag-history-aggregate-function/63863/2 "2022-09-07T23:41:03Z")
Specifically, the objects in question are a [`BlockContext`](https://files.inductiveautomation.com/sdk/javadoc/ignition81/8.1.20/com/inductiveautomation/ignition/gateway/sqltags/history/query/processing/BlockContext.html) and a [`QueryContext`](https://files.inductiveautomation.com/sdk/javadoc/ignition81/8.1.20/com/inductiveautomation/ignition/gateway/sqltags/history/query/processing/QueryContext.html). We can definitely get the manual updated with more information. ---
**Author:** ![tyler.bennett](https://avatars.discourse-cdn.com/v4/letter/t/f04885/32.png) [@tyler.bennett](https://forum.inductiveautomation.com/u/tyler.bennett)\ **Post date:** [September 8, 2022, 12:09am UTC](https://forum.inductiveautomation.com/t/how-to-use-previousrawvalue-and-previousblockresults-in-a-custom-tag-history-aggregate-function/63863/3 "2022-09-08T00:09:18Z")
A few other items that I discovered with testing and are covered in the documentation but are easy to miss… - You can write your own key/value pairs to the blockContext dictionary and these persist across evaluation of samples within a given time window (block), blockContext is reset for each time window (block). - You can write your own key/value pairs to the queryContext dictionary and these persist across evaluation of remaining samples for all blocks (does not reset). Example Usage: ``` def print2log(qval, interpolated, finished, blockContext, queryContext): blockContextCount = int(blockContext.getOrDefault('count',0)) + 1 blockContext['count'] = blockContextCount queryContextCount = int(queryContext.getOrDefault('count',0)) + 1 queryContext['count'] = queryContextCount print '--- Query Sample: {} | Block ID: {} | Block Sample: {} ---'.format(queryContextCount, blockContext.blockId, blockContextCount) if finished: print '----------' return "Output to wrapper.log" ``` Results: ```auto INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 1 | Block ID: 0 | Block Sample: 1 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 2 | Block ID: 0 | Block Sample: 2 --- INFO | jvm 2 | 2022/09/07 19:02:05 | ---------- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 3 | Block ID: 0 | Block Sample: 1 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 4 | Block ID: 0 | Block Sample: 2 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 5 | Block ID: 0 | Block Sample: 3 --- ... INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 53 | Block ID: 0 | Block Sample: 51 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 54 | Block ID: 0 | Block Sample: 52 --- INFO | jvm 2 | 2022/09/07 19:02:05 | ---------- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 55 | Block ID: 1 | Block Sample: 1 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 56 | Block ID: 1 | Block Sample: 2 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 57 | Block ID: 1 | Block Sample: 3 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 58 | Block ID: 1 | Block Sample: 4 --- INFO | jvm 2 | 2022/09/07 19:02:05 | ---------- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 59 | Block ID: 2 | Block Sample: 1 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 60 | Block ID: 2 | Block Sample: 2 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 61 | Block ID: 2 | Block Sample: 3 --- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 62 | Block ID: 2 | Block Sample: 4 --- INFO | jvm 2 | 2022/09/07 19:02:05 | ---------- INFO | jvm 2 | 2022/09/07 19:02:05 | --- Query Sample: 63 | Block ID: 3 | Block Sample: 1 --- ``` @PGriffith I noticed that the Block ID of 0 (zero) is used for two different blocks, not sure if that is a bug. I’ll investigate further. ---
**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:** [September 8, 2022, 3:25pm UTC](https://forum.inductiveautomation.com/t/how-to-use-previousrawvalue-and-previousblockresults-in-a-custom-tag-history-aggregate-function/63863/4 "2022-09-08T15:25:02Z")
> [@tyler.bennett](#): > > @paul-griffith I noticed that the Block ID of 0 (zero) is used for two different blocks, not sure if that is a bug. I’ll investigate further. It's entirely possible it's a bug. As you may have noticed, this feature hasn't gotten much attention since it was first implemented.