Element-wise difference between two arrays in dataview

[mika_long]

What I’m trying to do

I use inline metadata such as start:: 09:30 and end:: 10:30 to keep track and log the time I spend for each task in my daily note. My notes look something like

• (start:: 09:30) reading Cleveland and McGill 1984 (end:: 10:30)
• (start:: 13:45) generate stimuli with altair (end:: 14:45)

This will give me an array if I query inline using this.start or this.end. I want to be able to calculate the element-wise difference between these two arrays, such that if I type in the following dataview command,

Table 
start, end, (end - start) as duration
where file = this.file

I will be able to get a table of the start time, end time, and duration I’ve spent on each task for each day. Ideally, I also want something like a summation across all task durations, but I am currently stuck at the first step of each trying to calculate the element-wise difference between two arrays.

Things I have tried

I’ve looked into the documentation file for dataview as well as searched on this forum and reddit for a while, but I think the solutions I’ve encountered all involve some kind of javascript forEach loop. Is it possible to perform element-wise differences between two arrays in dataview?

[anon63144152]

Not got Obsidian on this Mac to test, but does FLATTEN help?

```dataview
TABLE 
L.start,
L.end,
L.end-L.start
WHERE file.name = this.file.name
FLATTEN file.lists as L
```

[anon63144152]

This works… but a hack:

- (start:: 09h15m) reading Cleveland and McGill 1984 (end:: 10h33m)
- (start:: 12h45m) generate stimuli with altair (end:: 14h47m)

```dataview
TABLE WITHOUT ID
L.start AS Start,
L.end AS End,
L.end - L.start AS Duration
WHERE file.name = this.file.name
FLATTEN file.lists as L
```

EDIT: This date and timestamp also works:

- (start:: 2023-04-11T09:15) reading Cleveland and McGill 1984 (end:: 2023-04-11T10:33)
- (start:: 2023-04-11T12:15) generate stimuli with altair (end:: 2023-04-11T19:21)

```dataview
TABLE WITHOUT ID
L.start AS Start,
L.end AS End,
L.end - L.start AS Duration
WHERE file.name = this.file.name
FLATTEN file.lists as L
```

[holroy]

@mika_long

Is it possible to perform element-wise differences between two arrays in dataview?

The common solution is to flatten the arrays, and then do the calculation on separate entities. Like suggested by @anon63144152 .

Another issues related to your code is that just the “HH:mm” isn’t considered a timestamp, so I’ve earlier suggested to add a “random” date part in front to make it into a proper date. Your query could then look like:

```dataview
TABLE WITHOUT ID item.start, item.end, duration
FLATTEN file.lists as item
FLATTEN (date("2023-01-01T" + item.end) -
         date("2023-01-01T" + item.start)) as duration
WHERE file.path = this.file.path
```

Back to your original question, it’s hard to traverse two arrays in parallell using dataview (especially in a DQL query). It can be done using indexes with some very convoluted code, but I wouldn’t recommend doing that. It’s a little easier in dataviewjs, but you’re still running the risk of the arrays shifting positions so that you’re suddenly have a misalignment of your data.

So in general, although it theoretically can be done, it’s better to use FLATTEN on the list and keep them gathered within that item scope.