# Using integer cycle point as an index to a list of parameters **URL:** \ **Category:** Cylc Support\ **Created:** [November 30, 2023, 9:26am UTC](https://cylc.discourse.group/t/using-integer-cycle-point-as-an-index-to-a-list-of-parameters/827 "2023-11-30T09:26:38Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![stewells](https://avatars.discourse-cdn.com/v4/letter/s/a4c791/32.png) [@stewells](https://cylc.discourse.group/u/stewells)\ **Post date:** [November 30, 2023, 9:26am UTC](https://cylc.discourse.group/t/using-integer-cycle-point-as-an-index-to-a-list-of-parameters/827/1 "2023-11-30T09:26:39Z")
Hi, I am just getting started using cycle points, and trying to cycle over a workflow where each iteration is assigned a specific variable to be called by the tasks (specifically a date as a string). I can run a single iteration by defining one of the cylc parameters to be the datestring, and then calling this within the tasks. However, I would like to be able to provide a list of dates that could be cycled over one after the other (not all together). Can I use the integer cylcing to index the list of dates and pick one for each cycle. Or perhaps there is a better alternative to achieve the same outcome? Many thanks, ---
**Author:** ![MetRonnie](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/metronnie/32/125_2.png) [@MetRonnie](https://cylc.discourse.group/u/MetRonnie)\ **Post date:** [November 30, 2023, 11:36am UTC](https://cylc.discourse.group/t/using-integer-cycle-point-as-an-index-to-a-list-of-parameters/827/2 "2023-11-30T11:36:21Z")
I am not sure what you are trying to describe here, but here are a couple of possible pointers for help (I am assuming you are using Cylc 8): - [The datetime cycling tutorials](https://cylc.github.io/cylc-doc/latest/html/tutorial/scheduling/datetime-cycling.html) if you haven’t already gone through them - You can use the `CYLC_TASK_CYCLE_POINT` environment variable in task runtime scripts. This is the current cycle point of the task at runtime. See [here](https://cylc.github.io/cylc-doc/latest/html/reference/job-script-vars/index.html) for the full list of environment variables - You can also use the `isodatetime` command to fiddle about with datetimes in the task script. Try `isodatetime --help` for info. Do you have a workflow file you can share so we can better understand? ---
**Author:** ![wxtim](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/wxtim/32/151_2.png) [@wxtim](https://cylc.discourse.group/u/wxtim)\ **Post date:** [November 30, 2023, 11:44am UTC](https://cylc.discourse.group/t/using-integer-cycle-point-as-an-index-to-a-list-of-parameters/827/3 "2023-11-30T11:44:43Z")
If you want to iterate over a list of dates I’d use date-time cycling, not integer. I’m guessing that your workflow might look a bit like: ```auto [scheduling] initial cycle point = 1066 stop after cycle point = 1086 [[graph]] # Create a dependency on the previous task P1Y = my_task[-P1Y] => my_task [runtime] [[my_task]] script = """ # Demo of how wierd a format isodatetime could output. TIME_POINT=$(isodatetime "$CYLC_TASK_CYCLE_POINT" --print-format "YEAR=%Y MONTH=%m DAY=%d") # Run your script: my_script" --date="${TIME_POINT}" ``` Is there any particular reason why the tasks need to be sequential? Does one produce data for the next or are you just wanting to avoid overwhealming a computer with to many tasks? ---
**Author:** ![stewells](https://avatars.discourse-cdn.com/v4/letter/s/a4c791/32.png) [@stewells](https://cylc.discourse.group/u/stewells)\ **Post date:** [November 30, 2023, 11:59am UTC](https://cylc.discourse.group/t/using-integer-cycle-point-as-an-index-to-a-list-of-parameters/827/4 "2023-11-30T11:59:57Z")
Thanks for the quick response. This looks like it would do what I’m after, thank you! I was originally thinking along the lines of having ```auto [cylc] [[parameters]] originTime = '20180812', ''20180912', ``` and then each iteration of the workflow would use the next originTime in the list (using the integer cycle point as a way to pick the right originTime to apply in the tasks. However, the dates are invariably consecutive/regular so using your above suggestion works nicely. Each cycle currently needs to be sequential to prevent too many simultaneous attempts to access a database by some of the tasks - this is why I haven’t used the above parameter setup and then defined the graph as eg ```auto A => B => C ``` However, if I understand correctly, a careful choice of when the next cycle is triggered (ie as soon as the task requiring the database is complete) could streamline the cycling? Many thanks, ---
**Author:** ![wxtim](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/wxtim/32/151_2.png) [@wxtim](https://cylc.discourse.group/u/wxtim)\ **Post date:** [November 30, 2023, 12:59pm UTC](https://cylc.discourse.group/t/using-integer-cycle-point-as-an-index-to-a-list-of-parameters/827/5 "2023-11-30T12:59:57Z")
### Direct answer > However, if I understand correctly, a careful choice of when the next cycle is triggered (ie as soon as the task requiring the database is complete) could streamline the cycling? Yes ### Detailed explanation If you had something like: ```auto database_heavy[-P1Y] => database_heavy first_task => database_heavy => something_else ``` You would end up with only one `database_heavy` task at a time. ### Alternative way of doing it: Queues Alternatively (if “too many simultaneous attempts to access a database” \> 1), you could do something like ```auto [scheduling] [[queues]] [[[database_use]]] limit = 2 members = database_heavy ``` ### Unrelated point: Cycle point format It also occurs to me to mention that you can set the Cycle point format [Workflow Configuration — Cylc 8.6.0 documentation](https://cylc.github.io/cylc-doc/stable/html/reference/config/workflow.html#flow.cylc%5Bscheduler%5Dcycle%20point%20format) - which might save you some messing around with `isodatetime`. Whatever you do, Datetime Cycling is pretty close to Cylc’s Raison d’etre, and using parameters to iterate over datetimes is a bit of an anti-pattern. ---
**Author:** ![stewells](https://avatars.discourse-cdn.com/v4/letter/s/a4c791/32.png) [@stewells](https://cylc.discourse.group/u/stewells)\ **Post date:** [November 30, 2023, 2:13pm UTC](https://cylc.discourse.group/t/using-integer-cycle-point-as-an-index-to-a-list-of-parameters/827/6 "2023-11-30T14:13:33Z")
Super, thank you so much for your help.