# Jsonata, modify some elements in an array of objects

**URL:** <https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216>\
**Category:** General\
**Tags:** jsonata\
**Created:** [13 April 2024 12:56 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216 "2024-04-13T12:56:49Z")\
**Posts on this page:** 15\
**Page:** 1

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [13 April 2024 12:56 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/1 "2024-04-13T12:56:49Z")

</div>

Speaking of the names of debug nodes, @Colin recently said

> [@Filter by change or x min](https://discourse.nodered.org/t/filter-by-change-or-x-min/87076/16):
>
> I imported a flow from here which bumped it up to a ridiculous value. I think node-red uses the current highest value as its base for new ones. What we need is a simple flow to renumber all the debug nodes in a flow to get it back down again. Well thats what I need anyway

And I too have "debug 2514" etc  
So I thought "yes a **simple** flow to rename them ..."

I can get a subset of flows.json, the offending nodes, using Jsonata in a change node

```auto
payload[type = "debug"][$match(name, /debug [0-9]{2}[0-9]*/)].{ "id": id, "name": name}

```

I think it means

- Operate on msg.payload.
- Records where type == "debug"
- And name is "debug " + 3 or more digits. Edit - That regex is actually 2 or more digits?
- Show me the id and name (If I omit the dot and after, it returns the complete debug nodes)

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/b/c/bc7450d63504c7730ce7c09147ba1af3eaebb9f8.png)

Beware: if you upload this flow, you too will have debug names \> 2500!

```auto
[{"id":"403d5b19c396432b","type":"inject","z":"cdc9555eb7388073","name":"go","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":90,"y":460,"wires":[["1e92a64c341706ef"]]},{"id":"1e92a64c341706ef","type":"file in","z":"cdc9555eb7388073","name":"flows.json","filename":".node-red/flows.json","filenameType":"str","format":"utf8","chunk":false,"sendError":false,"encoding":"none","allProps":false,"x":220,"y":460,"wires":[["b85e1bec4d611ad4"]]},{"id":"b85e1bec4d611ad4","type":"json","z":"cdc9555eb7388073","name":"","property":"payload","action":"","pretty":false,"x":350,"y":460,"wires":[["156e8643a18d7812"]]},{"id":"156e8643a18d7812","type":"change","z":"cdc9555eb7388073","name":"","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload[type = \"debug\"][$match(name, /debug [0-9]{2}[0-9]*/)].{ \"id\": id, \"name\": name}","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":500,"y":460,"wires":[["5a0b2209abc9f3b7"]]},{"id":"5a0b2209abc9f3b7","type":"debug","z":"cdc9555eb7388073","name":"debug 2519","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":670,"y":460,"wires":[]}]

```

gives me

```auto
[{"id":"2472d98c49fc78e8","name":"debug 156"},
{"id":"668298de4e1a94be","name":"debug 2514"},
{"id":"5a0b2209abc9f3b7","name":"debug 2519"}]

```

But how to modify the node names to "debug 0" + count?  
I suspect I need to use $map() and / or $merge() but I just can't get it to work for flows.json

---

<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [13 April 2024 13:10 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/2 "2024-04-13T13:10:30Z")

</div>

If you delete those debug nodes, deploy, restart node red and refresh the browser page then that may sort it.

---

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [13 April 2024 13:20 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/3 "2024-04-13T13:20:54Z")

</div>

Yes it does but it doesn't advance my Jsonata knowledge!

---

<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [13 April 2024 15:08 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/4 "2024-04-13T15:08:10Z")

</div>

You definitely picked a tricky one this time

```auto
(
    $debug := $$.payload[$contains($.name, /debug \d*/)].id;
    $reduce($$.payload, function($acc, $k) { 
        $k.id in $debug ? (
            {"data": $append($acc.data,$k ~> |$|{"name": "debug " & $acc.count}|),
            "count": $acc.count + 1 }
        ) : (
            {"data": $append($acc.data,$k),
            "count": $acc.count }
        ) 
      }, {"data":[], "count":1}
    ).data
)

```

[edit] remove unneeded variable binding and function

---

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [13 April 2024 19:32 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/5 "2024-04-13T19:32:02Z")

</div>

That certainly seems to work, I end up with "debug 1" to "debug 11".  
It's going to take some study to try and understand what's going on.

Unfortunately I can't do a straightforward diff flows.json newflows.json because my flows.json has new lines and the new file doesn't.

I do have a working flow too, Jsonata to extract the iffy debug nodes and a sed command to edit the file. It feels like cheating to shell out to the OS, but of course the ability to do that is part of why Node-red is so useful.  
I once tried to get the powers to consider building sed/awk/bash etc ability into the change node like Jsonata is, for situations like this. It didn't go down well!

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/a/3/a3655514b76975ac5b2525df32da30f9925c0d83.png)

```auto
[{"id":"c5f8b30b53cb1fda","type":"group","z":"cdc9555eb7388073","name":"Use jsonata to assemple a list of \"debug [0-9]{3}[0-9]*\" nodes and sed to edit them","style":{"label":true},"nodes":["203c41e8b6075f7c","8597d919d8d47788","951d72920008289f","1ef6f40a85ec11be","eb5bbc2b54cda6d6","152f43d6a8e4ba33","fc9a1b0790b3d6fa","3799d1023fc7c885","9887ed66d6f09245","772f0dbfdd07c24a","21b40b8cb56d2520","cc1e8a1c53da4cbe"],"x":14,"y":299,"w":812,"h":202},{"id":"203c41e8b6075f7c","type":"inject","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"go","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":110,"y":340,"wires":[["8597d919d8d47788"]]},{"id":"8597d919d8d47788","type":"file in","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"flows.json","filename":".node-red/flows.json","filenameType":"str","format":"utf8","chunk":false,"sendError":false,"encoding":"none","allProps":false,"x":240,"y":340,"wires":[["951d72920008289f"]]},{"id":"951d72920008289f","type":"json","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"","property":"payload","action":"","pretty":false,"x":370,"y":340,"wires":[["1ef6f40a85ec11be"]]},{"id":"1ef6f40a85ec11be","type":"change","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload[type = \"debug\"][$match(name, /debug [0-9]{3}[0-9]*/)].{ \"id\": id, \"name\": name}","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":520,"y":340,"wires":[["152f43d6a8e4ba33","fc9a1b0790b3d6fa"]]},{"id":"eb5bbc2b54cda6d6","type":"debug","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"Result","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":730,"y":420,"wires":[]},{"id":"152f43d6a8e4ba33","type":"function","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"sed command","func":"const debugs = msg.payload\nlet cmd = \"sed -i '\"\n\nfor (var index in debugs) {\n const nn = Number(index) + 1\n debugs[index].newname = \"debug 0\" + nn\n const sub = \"s/\\\"\" + debugs[index].name + \"\\\"/\\\"\" + debugs[index].newname + \"\\\"/; \"\n cmd = cmd + sub\n}\n\ncmd += \"' .node-red/flows.json \"\nmsg.payload = cmd\nreturn msg;","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":140,"y":420,"wires":[["cc1e8a1c53da4cbe"]]},{"id":"fc9a1b0790b3d6fa","type":"debug","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"debug 2523","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":710,"y":340,"wires":[]},{"id":"3799d1023fc7c885","type":"exec","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","command":"","addpay":"payload","append":"","useSpawn":"false","timer":"","winHide":false,"oldrc":false,"name":"Run it","x":330,"y":420,"wires":[[],[],["9887ed66d6f09245"]]},{"id":"9887ed66d6f09245","type":"switch","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"rc == 0?","property":"payload.code","propertyType":"msg","rules":[{"t":"eq","v":"0","vt":"num"},{"t":"else"}],"checkall":"true","repair":false,"outputs":2,"x":460,"y":420,"wires":[["772f0dbfdd07c24a"],["21b40b8cb56d2520"]]},{"id":"772f0dbfdd07c24a","type":"change","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"Restart","rules":[{"t":"set","p":"payload","pt":"msg","to":"Now restart Node-Red and reload the page","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":600,"y":400,"wires":[["eb5bbc2b54cda6d6"]]},{"id":"21b40b8cb56d2520","type":"change","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"Error","rules":[{"t":"set","p":"payload","pt":"msg","to":"Something went wrong!","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":590,"y":440,"wires":[["eb5bbc2b54cda6d6"]]},{"id":"cc1e8a1c53da4cbe","type":"debug","z":"cdc9555eb7388073","g":"c5f8b30b53cb1fda","name":"debug 2525","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":270,"y":460,"wires":[]}]

```

---

<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [13 April 2024 21:09 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/6 "2024-04-13T21:09:58Z")

</div>

> [@jbudd](#):
>
> Unfortunately I can't do a straightforward diff flows.json newflows.json because my flows.json has new lines and the new file doesn't.

Surely you can pass the JS object through a JSON node and check `format JSON string` to add newlines/format.

Or use the `$string(object, true)` to format the object as a formatted JSON string.  
e.g.

```auto
(
    $debug := $$.payload[$contains($.name, /debug \d*/)].id;
    $string(
        $reduce($$.payload, function($acc, $k) { 
            $k.id in $debug ? (
                {"data": $append($acc.data,$k ~> |$|{"name": "debug " & $acc.count}|),
                "count": $acc.count + 1 }
            ) : (
                {"data": $append($acc.data,$k),
                "count": $acc.count }
            ) 
            }, {"data":[], "count":1}
        ).data,
        true
    )
)

```

---

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [13 April 2024 21:41 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/7 "2024-04-13T21:41:10Z")

</div>

> [@E1cid](#):
>
> Surely you can pass the JS object through a JSON node and check `format JSON string` to add newlines/format.

Umm. I certainly didn't think of doing this, but actually I still seem to get everything on a single line.

> [@E1cid](#):
>
> Or use the `$string(object, true)` ...

A diff command after this gives me

```auto
pi@zerotwogreen:~ $ diff -w .node-red/flows.json newflows
95c95
< "name": "Jsonata get \"debug nnn+\" nodes",
---
> "name": "debug 1",
115c115
< "name": "Use jsonata to assemple a list of \"debug [0-9]{3}[0-9]*\" nodes and sed to edit them",
---
> "name": "debug 2",
142c142
< "name": "Get list of debug nodes without jsonata",
---
> "name": "debug 3",
1275c1275
< "name": "debug 1",
---
> "name": "debug 4",
1923c1923
< "name": "debug 156",
---
> "name": "debug 5",
2034c2034
< "name": "debug 2514",
---
> "name": "debug 6",
etc

```

Which shows it's a bit overeager. The first three amendments are actually groups which happen to contain "debug" in the name.  
On the other hand, it drew my attention to a typo in "assemple"

I'm tremendously impressed so far 😀

A simple tweek to the regex in your first line, \d+ rather than \d\* eliminates those three substitutions.

```auto
$debug := $.payload[$contains($.name, /debug \d+/)].id;

```

---

<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [14 April 2024 11:45 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/8 "2024-04-14T11:45:02Z")

</div>

Looked at this again this morning, with fresh eyes.  
This also works and seems simple and less intensive

```auto
(
    $debug := $$.payload[$contains($.name, /debug \d+/)].id;
    $$.payload ~> |$| 
        $.id in $debug ? (
            {
                "name": "debug " & $map($debug, function($v, $i){
                    $.id = $v ? $i + 1
                })
            }
        ) 
    | ~> $string(true)
)
        

```

---

<div class="post-metadata">

**Author:** ![shrickus](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/shrickus/32/517_2.png) [@shrickus](https://discourse.nodered.org/u/shrickus)\
**Post date:** [14 April 2024 14:10 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/9 "2024-04-14T14:10:37Z")

</div>

If you don't mind having "holes" in the debug numbering sequence, you could just use the index of the node inside the flow array -- makes for a much simpler JSONata expression, using the [transform operator](http://docs.jsonata.org/other-operators#-------transform):

```auto
payload#$idx.(
    $ ~> | $[type='debug'] | { "name": name.$replace(/^debug (\d+)$/, 'debug ' & $idx) } |
)

```

Think of the transform as an inline stream editor (i.e. `sed`) that modifies data inside the stream but leaves the outer structure intact -- essentially the syntax says this:

`array of objs to transform` ~\> | `obj to be changed` | { `fld1: 'val1'`, `fld2: 'val2'`, etc.} |

(Notice that I have also used a non-greedy regex that only replaces names matching the default naming scheme)

Of course, this does not really help you if you have 1000's of nodes in your flows...

---

<div class="post-metadata">

**Author:** ![shrickus](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/shrickus/32/517_2.png) [@shrickus](https://discourse.nodered.org/u/shrickus)\
**Post date:** [14 April 2024 14:55 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/10 "2024-04-14T14:55:12Z")

</div>

Actually, I thought of a better way to do it without using the index... first build a list of just the debug nodes to be changed, and create a lookup table of the `{ id: 'debug #' }`

Then just transform the entire payload in-place, substituting the new names from the lookup table, if found:

```auto
(
    $dbgNodeIds := payload[type='debug' and name.$match(/^debug (\d+)$/)]#$idx.{id: 'debug ' & ($idx+1)};
    payload ~> | $ | { "name": $lookup($dbgNodeIds, id) ? $lookup($dbgNodeIds, id) : name } |
)

```

---

<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [14 April 2024 15:17 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/11 "2024-04-14T15:17:05Z")

</div>

I don't think the ternary after the lookup() is required

```auto
payload ~> | $ | { "name": $lookup($dbgNodeIds, id) } |

```

Should be all that is required.

---

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [14 April 2024 15:43 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/12 "2024-04-14T15:43:00Z")

</div>

> [@shrickus](#):
>
> If you don't mind having "holes" in the debug numbering sequence, you could just use the index of the node inside the flow array

Oh no, that would never do! 🙃

I am overwhelmed. No, honestly!

Going to have to insist on a blow by blow explanation, like this:

> [@shrickus](#):
>
> Think of the transform as an inline stream editor (i.e. `sed`) that modifies data inside the stream but leaves the outer structure intact -- essentially the syntax says this:
> 
> `array of objs to transform` ~\> | `obj to be changed` | { `fld1: 'val1'`, `fld2: 'val2'`, etc.} |

I started by 00Going Pascal assignment operator in Jsonata (without success) but then `| $ |` grabbed my eye. That can't mean anything, surely? 😀

I'm playing with [try.jsonata.org](https://try.jsonata.org) but every time I think I've grasped a concept and use it to build an expression it gives me a bloody nose.

Thanks for all the contributions!

---

<div class="post-metadata">

**Author:** ![shrickus](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/shrickus/32/517_2.png) [@shrickus](https://discourse.nodered.org/u/shrickus)\
**Post date:** [14 April 2024 15:52 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/13 "2024-04-14T15:52:11Z")

</div>

Oh right -- If the $lookup returns nothing, then the object name is not going to be transformed, is it? Good catch!

---

<div class="post-metadata">

**Author:** ![shrickus](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/shrickus/32/517_2.png) [@shrickus](https://discourse.nodered.org/u/shrickus)\
**Post date:** [14 April 2024 16:25 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/14 "2024-04-14T16:25:22Z")

</div>

> [@jbudd](#):
>
> Going to have to insist on a blow by blow explanation

How about this =\> [https://try.jsonata.org/PW05fSKqW](https://try.jsonata.org/PW05fSKqW)

```auto
( /* start of compound expression */
    $dbgNames := /* var to hold lookup table */
        payload[
            type='debug' /* filter for just debug nodes ... */
            and /* ... and ... */
            name.$match(/^debug (\d+)$/) /* names like "debug ####" */
        ]
        #$idx /* var to hold the array index number */
            .{ /* map operator - create a new obj for each node */
                id: 'debug ' & ($idx+1) /* key = node "id", value = indexed debug name */
            };

    payload ~> /* Now transform the entire flow array of nodes */
        | /* start of transform operator */
            $ /* set the "context" of the following expr to each node */
        | 
            { /* object with fields to replace the context object fields */
                "name": $lookup($dbgNames, id) /* lookup the new name -- if not found, nothing is changed */
            }
            ,[] /* optional list of fields names to be removed (fyi) */
        | /* end of transform operator */
) /* end of compound expression */

```

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [13 July 2024 16:25 UTC](https://discourse.nodered.org/t/jsonata-modify-some-elements-in-an-array-of-objects/87216/15 "2024-07-13T16:25:49Z")

</div>

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