remember previous json value in array - json

Question

I have a sorted array list and I wish to make a formatting decision depending on the value of a json bool in the previous iteration of the array. The code example uses the current value of igroup but I need to have a MARK on the first instance of igroup=true and then all subsequent igroup=true to be SPACE. To do this I need to know what the previous value of igroup was. It seems a variable to try and remember the prev value is not possible so I am at a loss as to how I can make this happen.
Code:
.result
| keys[] as $c
|
(
(.[$c].segments[0].lines | keys[]) as $l |
[
"line format",
( if .[$c].segments[0].lines[$l].igroup then "SPACE"
else "MARK" end ),
( [ .[$c].segments[0].lines[$l].products[].name ] | join(",")),
"end line format"
]
),
["END","0"]
| join("|")
example data:
{
"result": [
{
"cn": "abc",
"segments": [
{
"lines": [
{
"igroup": false,
"products": [
{
"name": "Should be MARK"
}
]
},
{
"igroup": false,
"products": [
{
"name": "Should be MARK"
},
{
"name": "Addon to MARK"
}
]
},
{
"igroup": true,
"products": [
{
"name": "Should be MARK First igroup=true BROKEN!!!"
}
]
},
{
"igroup": true,
"products": [
{
"name": "Should be SPACE !! After first igroup=true"
}
]
},
{
"igroup": true,
"products": [
{
"name": "Should be SPACE until next igroup=false"
}
]
},
{
"igroup": false,
"products": [
{
"name": "Should be MARK"
}
]
}
]
}
]
}
],
"id": 1
}
The output:
"line format|MARK|Should be MARK|end line format"
"line format|MARK|Should be MARK,Addon to MARK|end line format"
"line format|SPACE|Should be MARK First igroup=true BROKEN!!!|end line format"
"line format|SPACE|Should be SPACE !! After first igroup=true|end line format"
"line format|SPACE|Should be SPACE until next igroup=false|end line format"
"line format|MARK|Should be MARK|end line format"
"END|0"

Answer 1

There's a couple of approaches you could take, reduce over the indices so you could index into the array to check the values. But this requires keeping a separate reference to the original input.
Otherwise using foreach allows you to keep track of the previous igroup through the accumulator.
foreach .result[].segments[].lines[] as {$igroup,$products} (
[null,false]; # init: pair of previous and current value
[.[1],$igroup]; # update: update values
[
"line format",
if .[0] and .[0] == $igroup then "SPACE" else "MARK" end,
([$products[].name] | join(",")),
"end line format"
] # extract: the collection of values to output
), ["END",0] | join("|")
"line format|MARK|Should be MARK|end line format"
"line format|MARK|Should be MARK,Addon to MARK|end line format"
"line format|MARK|Should be MARK First igroup=true BROKEN!!!|end line format"
"line format|SPACE|Should be SPACE !! After first igroup=true|end line format"
"line format|SPACE|Should be SPACE until next igroup=false|end line format"
"line format|MARK|Should be MARK|end line format"
"END|0"
Tweak the output as needed.
jqplay

Answer 2

I was able to make some progress on my own but am still not happy with the result. I was able to use the index to check the prev arrays value. I dont like the 3 deep if-then-else-end blocks but at least it works. What it does do is allows me access to the multitude of other fields in the segments and lines arrays that the test data doesn't show.
.result
| keys[] as $c
|
(
(.[$c].segments[0].lines | keys[]) as $l |
[
( $l ),
( if $l > 0
then
( if .[$c].segments[0].lines[$l].igroup
then
( if .[$c].segments[0].lines[$l - 1].igroup
then "SPACE"
else "MARK" end
)
else "MARK" end
)
else "MARK" end
),
"line format",
( [ .[$c].segments[0].lines[$l].products[].name ] | join(",")),
"end line format"
]
),
["END","0"]
| join("|")
I will look into the solution above as an alternative.