Develop Reference

Given an array of Long values in Kotlin and a position parameter, when the position is in the middle of two of the array values, return the lowest

Spotify's lyrics API provides an Array of miliseconds to mark when the lyric line has changed. Having a Media Player that updates it's position every 50ms, how should i code in Kotlin the way to find the correct lyric line? The position param can be in the middle of two values of the array, so I want to get the lowest one of that two.
I tried to get the lowest value compared to the position parameter but lol, it will always be the first value of the Array... Silly fault of mine.

The problem is that I have a third one that indicates the range of that two value. For example: I have an Array of [45, 78, 125, 198]. If I pass the position param where it's value is 95, I want to return the 78 (that is the lowest value from itself, the position param and 125).
/** Input data for example (from your comment). */
val yourArray = arrayOf(45, 78, 125, 198)
val inputValue = 95
/** How to get needed index. */
val resultIndex = yourArray.indexOfLast { it < inputValue }.takeIf { it != -1 }
If you get resultIndex == null - it means you don't have value inside your array which lower then your inputValue.
I think it's simpler than find indexOfFirst and compare result later. And absolutely better and safer when sort() solution.

Insert the position param into the array, sort it, find its index and use it to get the closest value.
val array: MutableList<Long> = mutableListOf(4L, 9L, 5L, 1L)
val position = 7L
array.add(position)
println(array[array.sorted().indexOf(position) - 1])
Output: 5

If I correctly understand, you need simply use min function for compare two numbers in Kotlin and find the low one: link

Here’s a way to do it without having to make two copies of the list and doing a sort.
val foundIndex = lyricTimesList.indexOfFirst { it > inputTime }
val result = if (foundIndex == -1) lyricTimesList.size - 1 else foundIndex - 1
Note the result could be -1 if the input time is less than the first number in the list.

ArrayList.add() causing OutOfMemory error?

For the first time today, I've met an OutOfMemory Error. I'm trying to calculate moving averages out of some data into an ArrayList, and had a crash at the first .add() step. The method is shown below
public ArrayList<Long> getNdaySMA(List<HistoricalQuote> history, int range){
long sum =0;
long SMA = 0;
ArrayList<Long> SMAs = new ArrayList<Long>();
//realRange is made due to the differences in defining "range in calculation vs speech
//a 10 day range for day 9 is actually from prices of day0 to day9, inclusive
int realRange =range-1;
//First step, add in placeholder 0s for the days within the range that have no value
//so if 10 day range, we have 0-> 9
for (int i=0;i<i+realRange;i++){
SMAs.add(i,0L);
}
//Next, actually calculate the SMAs for i.e. day 10
for (int i =0;i<history.size();i++){
//should be k<10, 0......9 = 10 days
for(int k=i+realRange;k==i;k--){
//Sum first from k=i+range-1 , go down to i.
//This should give us a value of RANGE
sum +=history.get(k).getClose().longValue();
}
//after summing up, we add calculate SMA and add it to list of SMAs
SMA = sum/range;
//we add the corresponding SMA to index i+range, made up of values calculated from before it
//to excel
SMAs.add(i+realRange,SMA);
sum =0;
}
return SMAs;
}
The stacktrace is as follows
java.lang.OutOfMemoryError
at java.util.ArrayList.add(ArrayList.java:154)
at com.xu.investo.MethodDatabase.getNdaySMA(MethodDatabase.java:46)
Where Line 46 refers to
SMAs.add(i,0L);
Is this error occuring due to the use of the Long number format? Any suggestions are welcome.

looks like infinite loop:
for (int i=0;i<i+realRange;i++)
i will always be less then i+realRange for realRange greater then zero:

I think I've identified the problem.
I may have created an infinite loop at this line
for (int i=0;i<i+realRange;i++){
SMAs.add(i,0L);
}

Google Sheets API v4 - How to get the last row with value?

How to get the last row with value in the new Google Sheets API v4 ?
i use this to get a range from a sheet:
mService.spreadsheets().values().get("ID_SHEET", "Sheet1!A2:B50").execute();
how to detect the last row with value in the sheet ?

You can set the range to "A2:D" and this would fetch as far as the last data row in your sheet.

I managed to get it by counting the total rows from current Sheets.
Then append the data to the next row.
rowcount = this.mService.spreadsheets().values().get(spreadsheetId, range).execute().getValues().size()

Rather than retrieving all the rows into memory just to get the values in the last row, you can use the append API to append an empty table to the end of the sheet, and then parse the range that comes back in the response. You can then use the index of the last row to request just the data you want.
This example is in Python:
#empty table
table = {
'majorDimension': 'ROWS',
'values': []
}
# append the empty table
request = service.spreadsheets().values().append(
spreadsheetId=SPREADSHEET_ID,
range=RANGE_NAME,
valueInputOption='USER_ENTERED',
insertDataOption='INSERT_ROWS',
body=table)
result = request.execute()
# get last row index
p = re.compile('^.*![A-Z]+\d+:[A-Z]+(\d+)$')
match = p.match(result['tableRange'])
lastrow = match.group(1)
# lookup the data on the last row
result = service.spreadsheets().values().get(
spreadsheetId=SPREADSHEET_ID,
range=f'Sheetname!A{lastrow}:ZZ{lastrow}'
).execute()
print(result)

😢 Google Sheets API v4 does not have a response that help you to get the index of the last written row in a sheet (row that all cells below it are empty). Sadly, you'll have to workaround and fetch all sheet rows' into memory (I urge you to comment if I'm mistaken)
Example:
spreadsheet_id = '1TfWKWaWypbq7wc4gbe2eavRBjzuOcpAD028CH4esgKw'
range = 'Sheet1!A:Z'
rows = service.spreadsheets().values().get(spreadsheetId=spreadsheet_id, range=range).execute().get('values', [])
last_row = rows[-1] if rows else None
last_row_id = len(rows)
print(last_row_id, last_row)
Output:
13 ['this', 'is ', 'my', 'last', 'row']
💡 If you wish to append more rows to the last row, see this

You don't need to. Set a huge range (for example A2:D5000) to guarantee that all your rows will be located in it. I don't know if it has some further impact, may be increased memory consumption or something, but for now it's OK.
private List<String> getDataFromApi() throws IOException {
String spreadsheetId = "1BxiMVs0XRA5nFMdKvBdBZjgmUUqptlbs74OgvE2upms";
String range = "A2:D5000";
List<String> results = new ArrayList<String>();
ValueRange response = this.mService.spreadsheets().values()
.get(spreadsheetId, range)
.execute();
List<List<Object>> values = response.getValues();
if (values != null) {
results.add("Name, Major");
for (List row : values) {
results.add(row.get(0) + ", " + row.get(3));
}
}
return results;
}
Look at the loop for (List row : values). If you have two rows in your table you will get two elements in values list.

Have a cell somewhere that doesn't interfere with your datarange with =COUNTA(A:A) formula and get that value.
In your case
=MAX(COUNTA(A:A50),COUNTA(B:B50))
?
If there could be empty cells inbetween the formula would be a little more tricky but I believe it saves you some memories.

2022 Update
I I don’t know if this will be relevant for someone in 2022, but now you can do it differently.
You can just set next value as range :
const column = "A"
const startIndex = 2
const range = column + startIndex + ":" + column
In resolve you get all data in column and range with last index.
I tested it on js and php

Following Mark B's answer, I created a function that performs a dummy append and then extracts the last row info from the dummy append's response.
def get_last_row_with_data(service, value_input_option="USER_ENTERED"):
last_row_with_data = '1'
try:
dummy_request_append = service.spreadsheets().values().append(
spreadsheetId='<spreadsheet id>',
range="{0}!A:{1}".format('Tab Name', 'ZZZ'),
valueInputOption='USER_ENTERED',
includeValuesInResponse=True,
responseValueRenderOption='UNFORMATTED_VALUE',
body={
"values": [['']]
}
).execute()
a1_range = dummy_request_append.get('updates', {}).get('updatedRange', 'dummy_tab!a1')
bottom_right_range = a1_range.split('!')[1]
number_chars = [i for i in list(bottom_right_range) if i.isdigit()]
last_row_with_data = ''.join(number_chars)
except Exception as e:
last_row_with_data = '1'
return last_row_with_data

Fragment crash: IndexOutOfBoundsException: Invalid index x, size is x after updating my database [duplicate]

When I do
ArrayList<Integer> arr = new ArrayList<Integer>(10);
arr.set(0, 1);
Java gives me
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.rangeCheck(Unknown Source)
at java.util.ArrayList.set(Unknown Source)
at HelloWorld.main(HelloWorld.java:13)
Is there an easy way I can pre-reserve the size of ArrayList and then use the indices immediately, just like arrays?

How about this:
ArrayList<Integer> arr = new ArrayList<Integer>(Collections.nCopies(10, 0));
This will initialize arr with 10 zero's. Then you can feel free to use the indexes immediately.

Here's the source from ArrayList:
The constructor:
public ArrayList(int initialCapacity)
{
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity);
this.elementData = new Object[initialCapacity];
}
You called set(int, E):
public E set(int index, E element)
{
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
Set calls rangeCheck(int):
private void rangeCheck(int index)
{
if (index >= size) {
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
}
It may be subtle, but when you called the constructor, despite initializing an Object[], you did not initialize size. Hence, from rangeCheck, you get the IndexOutOfBoundsException, since size is 0. Instead of using set(int, E), you can use add(E e) (adds e of type E to the end of the list, in your case: add(1)) and this won't occur. Or, if it suits you, you could initialize all elements to 0 as suggested in another answer.

I believe the issue here is that although you have suggested the allocated space of entries in the Array, you have not actually created entries.
What does arr.size() return?
I think you need to use the add(T) method instead.

Programming aside, what you are trying to do here is illogical.
Imagine an empty egg carton with space for ten eggs. That is more or less what you have created. Then you tell a super-precise-and-annoying-which-does-exactly-what-you-tell-him robot to replace the 0th egg with another egg. The robot reports an error. Why? He can't replace the 0th egg, because there is no egg there! There is a space reserved for 10 eggs, but there are really no eggs inside!

You could use arr.add(1), which will add 1 in the first empty cell, i.e. the 0-indexed one.
Or you could create your own list:
public static class PresetArrayList<E> extends ArrayList<E> {
private static final long serialVersionUID = 1L;
public PresetArrayList(int initialCapacity) {
super(initialCapacity);
addAll(Collections.nCopies(initialCapacity, (E) null));
}
}
Then:
List<Integer> list = new PresetArrayList<Integer>(5);
list.set(3, 1);
System.out.println(list);
Prints:
[null, null, null, 1, null]

This is not an Java-specific answer but an data structure answer.
You are confusing the Capacity concept with the Count (or Size) one.
Capacity is when you tell the list to reserve/preallocate a number of slots in advance (in this ArrayList case, you are saying to it create an array of 10 positions) in its' internal storage. When this happens, the list still does not have any items.
Size (or Count) is the quantity of items the list really have. In your code, you really doesn't added any item - so the IndexOutOfBoundException is deserved.

While you can't do what you want with arraylist, there is another option: Arrays.asList()

Capacity is used to prepare ArrayLists for expansion. Take the loop
List<Integer> list = new ArrayList<>();
for(final int i = 0; i < 1024; ++i) {
list.add(i);
}
list starts off with a capacity of 10. Therefore it holds a new Integer[10] inside. As the loop adds to the list, the integers are added to that array. When the array is filled and another number is added, a new array is allocated twice the size of the old one, and the old values are copied to the new ones. Adding an item is O(1) at best, and O(N) at worst. But adding N items will take about 2*1024 individual assignments: amortized linear time.
Capacity isn't size. If you haven't added to the array list yet, the size will be zero, and attempting to write into the 3rd element will fail.

How does Java implement the moveToPrevious method on Cursor?

I came across a method on Cursor called moveToPrevious().
I had previously read an article which suggested that implementing a backwards version of the C SQLite step command would be hard / impossible:
... asking for an sqlite3_step_backward() button is really like expecting your symbolic debugger to be able to run backwards or to "undo" its execution back to the previous breakpoint. Nobody reasonably expects debuggers to be able to do this, so you shouldn't expect SQLite to be able to sqlite3_step_backward() either.
Is an Android cursor a wrapper around SQLite or some kind of a independent implementation?
How how have thay made this moveToPrevious command?

The Android Cursor class indeed reads all result records into memory first, and then allows you to step through them randomly.
(This is why there is the 1 MB limit on data in a cursor.)

Cursor interface provides random read-write access to the result set returned by a database query. Cursor implementations are not required to be synchronized so code using a Cursor from multiple threads should perform its own synchronization when using the Cursor.
Cursor: Retrieving data from SQLite databases in Android is done using Cursors. The Android SQLite query method returns a Cursor object containing the results of the query.Cursors store query result records in rows and grant many methods to access and iterate through the records.To use Cursors android.database.Cursor must be imported.
http://developer.android.com/reference/android/database/Cursor.html
Check the source here
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.2.2_r1/android/database/Cursor.java/
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.2.2_r1/android/database/AbstractCursor.java/
Look at the line 248 in the link
248 public final boolean moveToPrevious() {
249 return moveToPosition(mPos - 1);
// mPos looks like is the index here which is an int
250 }
moveToPosition
195 public final boolean moveToPosition(int position) {
196 // Make sure position is not past the end of the cursor
197 final int count = getCount();
198 if (position >= count) {
199 mPos = count;
200 return false;
201 }
202
203 // Make sure position isn't before the beginning of the cursor
204 if (position < 0) {
205 mPos = -1;
206 return false;
207 }
208
209 // Check for no-op moves, and skip the rest of the work for them
210 if (position == mPos) {
211 return true;
212 }
getCount()
Returns the current position of the cursor in the row set. The value is zero-based. When the row set is first returned the cursor will be at positon -1, which is before the first row. After the last row is returned another call to next() will leave the cursor past the last entry, at a position of count().
Returns:
the current cursor position.