Sorting a JSON based on date

Question

I want to sort a json based on the date inside period but it also contains other string(MAT TY and MAT YA) values which we have to keep in the front of list always(MAT TY first then MAT YA after) and the sorted items after that so how do i do it? Here's the JSON response:

 [{

        "Period": "MAT YA",
        "StartUnit": null,
        "EndUnit": null,

    },
    {

        "Period": "DEC 2018",
        "StartUnit": null,
        "EndUnit": null,

    },
    {

        "Period": "NOV 2018",
        "StartUnit": null,
        "EndUnit": null,

    },
    {

        "Period": "SEP 2018",
        "StartUnit": null,
        "EndUnit": null,

    },
    {

        "Period": "JUN 2019",
        "StartUnit": null,
        "EndUnit": null,

    },
    {

        "Period": "MAT TY",
        "StartUnit": null,
        "EndUnit": null,
    },
    {

        "Period": "MAT YA",
        "StartUnit": null,
        "EndUnit": null,

    },
    {

        "Period": "MAT YA",
        "StartUnit": null,
        "EndUnit": null,

    },
    {

        "Period": "MAT TY",
        "StartUnit": null,
        "EndUnit": null,

    }
]

I know Comparator like this:

myDateList.sortWith(Comparator { s1, s2 -> myDateList.indexOf(s1).compareTo(myDateList.indexOf(s2))})

So how can i convert it to meet the above requirement?

Update: The custom comparator:

 private fun customSortFunction(mydateList: ArrayList<String>){
        val sdf = SimpleDateFormat("MMM yyyy")
        val comparator = Comparator<String> { date1, date2 ->
            if (date1 == "MAT TY") return@Comparator -1
            if (date2 == "MAT TY") return@Comparator 1
            if (date1 == "MAT YA") return@Comparator -1
            if (date2 == "MAT YA") return@Comparator 1

            val date1Formatted = sdf.parse(date1)
            val date2Formatted = sdf.parse(date2)
            return@Comparator date1Formatted.compareTo(date2Formatted)
        }

        mydateList.sortWith(comparator)
        Log.e(TAG, "Date list: "+ mydateList)
    }

StackTrace:

 java.lang.IllegalArgumentException: Comparison method violates its general contract!
        at java.util.TimSort.mergeHi(TimSort.java:899)
        at java.util.TimSort.mergeAt(TimSort.java:516)
        at java.util.TimSort.mergeCollapse(TimSort.java:441)
        at java.util.TimSort.sort(TimSort.java:245)
        at java.util.Arrays.sort(Arrays.java:1523)
        at java.util.Collections.sort(Collections.java:238)
        at kotlin.collections.CollectionsKt__MutableCollectionsJVMKt.sortWith(MutableCollectionsJVM.kt:34)
        at com.abc.ShareStoryFragment.customSortFunction(ShareStoryFragment.kt:429)

And the 429th line is:

mydateList.sortWith(comparator)

Mydatelist values:

[SEP 2019, JUL 2019, AUG 2019, JUN 2019, MAY 2019, APR 2019, MAT TY, MAR 2019, FEB 2019, MAT YA, NOV 2018, SEP 2018, DEC 2018, OCT 2018, JAN 2019, FEB 2019, SEP 2018, JAN 2019, NOV 2018, OCT 2018, DEC 2018, MAT YA, MAT YA, NOV 2018, MAR 2019, MAT TY, SEP 2018, OCT 2018, DEC 2018, APR 2019, JUL 2019, APR 2019, SEP 2019, AUG 2019, MAY 2019, AUG 2019, MAT TY, JAN 2019, FEB 2019, JUN 2019, MAR 2019, MAY 2019, SEP 2019, JUL 2019, JUN 2019, APR 2019, MAR 2019, FEB 2019, MAY 2019, JAN 2019, MAT YA, MAT TY, AUG 2019, DEC 2018, SEP 2019, JUL 2019, NOV 2018, JUN 2019, SEP 2018, OCT 2018, SEP 2019, AUG 2019, JUL 2019, MAY 2019, APR 2019, JUN 2019, MAT TY, MAR 2019, FEB 2019, MAT YA, DEC 2018, OCT 2018, NOV 2018, JAN 2019, SEP 2018, MAT YA, SEP 2018, DEC 2018, OCT 2018, NOV 2018, FEB 2019, JAN 2019, MAR 2019, APR 2019, MAT TY, JUL 2019, MAY 2019, JUN 2019, SEP 2019, AUG 2019, JUN 2019, AUG 2019, SEP 2019, OCT 2018, JUL 2019, SEP 2018, MAY 2019, MAT TY, JAN 2019, NOV 2018, DEC 2018, FEB 2019, MAR 2019, APR 2019, MAT YA]

Please help.

@Md.Asaduzzaman Normal sorting i can do but how do i keep the MAT TY values in top and the date is only in Month Year format. — Cosmic Dev, Dec 24 '19 at 11:53
You can create a special case in your custom comparator. Can you post code on how you're sorting the list? — Christilyn Arjona, Dec 24 '19 at 20:26
Try https://docs.oracle.com/javase/8/docs/api/java/time/YearMonth.html#parse-java.lang.CharSequence-java... That'll parse it into a YearMonth. You just need to make the DateTimeFormatter. — sak, Dec 26 '19 at 03:32

score 3 · Accepted Answer · answered Dec 26 '19 at 17:18

The comparison logic described does not follow the contract. If there is no branch covering when both strings are "MAT YA" or "MAT TY", you can end up with situations where A > B and B > A. You need another condition up top that handles when both strings are the same:

private val val sdf = SimpleDateFormat("MMM yyyy")

fun compare(s1: String?, s2: String?): Int = when {
  s1 == s2 -> 0
  s1 == "MAT TY" -> -1
  s2 == "MAT TY" -> 1
  s1 == "MAT YA" -> -1
  s2 == "MAT YA" -> 1
  s1 == null -> 1
  s2 == null -> -1
  else -> sdf.parse(s1).compareTo(sdf.parse(s2))
}

Christilyn Arjona · Answer 2 · 2019-12-26T06:46:59.977

1

Here is a custom comparator that meets your need:

val sdf = SimpleDateFormat("MMM yyyy")
val stringList = arrayListOf(
        "JUN 2019",
        "MAT YA",
        "SEP 2018",
        "MAT YA",
        "MAT TY",
        "NOV 2018"
)

val comparator = Comparator<String> { date1, date2 ->
    if (date1 == "MAT TY") return@Comparator -1
    if (date2 == "MAT TY") return@Comparator 1
    if (date1 == "MAT YA") return@Comparator -1
    if (date2 == "MAT YA") return@Comparator 1

    val date1Formatted = sdf.parse(date1)
    val date2Formatted = sdf.parse(date2)
    return@Comparator date1Formatted.compareTo(date2Formatted)
}

stringList.sortWith(comparator)
println(stringList)

This results in:

[MAT TY, MAT YA, MAT YA, SEP 2018, NOV 2018, JUN 2019]

edited Dec 26 '19 at 06:46

answered Dec 26 '19 at 04:44

Christilyn Arjona

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and what about sorting the dates ? Nov 2018 should be ahead of jun 2019 – Cosmic Dev Dec 26 '19 at 06:40
@CosmicDev I've edited my answer to account for actual dates comparison. Hope it helps – Christilyn Arjona Dec 26 '19 at 06:47
getting an error of: java.lang.IllegalArgumentException: Comparison method violates its general contract! – Cosmic Dev Dec 26 '19 at 06:56
@CosmicDev Which line are you getting the error? also, could you maybe update your post with your new implementation so I could see – Christilyn Arjona Dec 26 '19 at 06:58
Just did please check – Cosmic Dev Dec 26 '19 at 07:09
@CosmicDev Weird. I tried the code and I'm not getting any errors like yours. – Christilyn Arjona Dec 26 '19 at 07:32
are you trying in android or any kotlin compiler? – Cosmic Dev Dec 26 '19 at 07:34
you are right on your part, the code is working fine, the problem seems to be with the arraylist i am passing – Cosmic Dev Dec 26 '19 at 07:50
@CosmicDev what are you passing in your `customSortFunction` function? – Christilyn Arjona Dec 26 '19 at 08:05
An String ArrayList: the values are: My date list: [SEP 2019, JUL 2019, AUG 2019, JUN 2019, MAY 2019....] i have updated the complete values in question. – Cosmic Dev Dec 26 '19 at 08:41
I found out that's the length of the ArrayList – Cosmic Dev Dec 26 '19 at 08:52

Sorting a JSON based on date

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