I'm using Core Data with an NSFetchedResultsController. My data consists of many students and lesson dates. I set my Predicate and Sort Descriptors up to return a sorted lists of lessons for a particular student. I sort ascending or defending, and my table view is loaded and happy.
However, at times, I want to return only the previous two lessons, sorted ascending. How in the world can I construct a NSFetchRequest to only return an array of two items?
I've been trying to fool the table view by modifying rows and sections... and yes, it is getting tangled up and clunky.
It seems I need to nest NSFetchRequests inside of the NSFetchedResultsController. First fetching and getting the number of total items / sections. And then just getting the last two objects when sorting ascending. How do I limit the results to the last two items when I don't know how many items there are when setting up the NSFetchRequest?
Thanks
Just tell the fetch request how many you want:
[fetchRequest setFetchLimit:2];
Results will be sorted according to your sort descriptor(s), and you'll get the first two results.
Related
I have a huge epidemiological dataset containing registry data with pathology reports and clinical information. I have merged several files into one masterfile in order to get all information from one file. Every patient is assigned an unique ID-number. Each patient can have several reports and hence the same ID number can be repeated several times in the ID column. For each ID entry = new row (= pathology or clinical report) there is a date of that sample/information reported.
My goal is to be able to read all pathology/clinical info for a particular ID within one row.
By sorting the IDs, I get a clear picture of the number of each ID that has been entered. The problem arises when there are several reports = multiple rows with identical ID because the dates within this one patients with several IDs = rows do not match. The dates come from pathology (sample date, answer date, clinical info date etc). The dates from pathology and clinical within one patient does not have to match exactly on the day but still within a reasonable timeframe e.g. within 1-2 months. This is best illustrated with an example.
I want to sort the columns so that dates from a particular row match together. I am sure there is a way to do that but I cannot figure it out.
Thanks in advance
The issue of mismatching records seems to arise once the two separate tables are merged into one. In order to fix this, there are several options you can take:
Re-do the merge but strengthen the way in which the tables are joined on.
Instead of only merging based on ID, see if there is another field that could easily connect the records, perhaps a medical record #, case #, or event #, and merge the tables based on this new field AND ID. This would be the strongest solution, however it will only work if you can find said field to strengthen the link.
A separate solution would be to first sort the original tables based on the dates so that they match up and then re-merging them together.
In theory this should solve your problem as I assume currently when matching up the two separate tables it is grabbing the first instance of patient X01 from both tables and matching them together. This can be confirmed by checking the merged query and looking to see if the mismatched records are in the same order as presented in the original tables. This is not perfect, as it relies on no clinical dates occurring between pathology dates for the record, so I would proceed with caution.
And to address your concern about losing track of ID's with multiple rows, this should not matter as in the end result after merged you can then sort by ID, however you can add multiple levels of sort by selecting the data and going to Data -> Sort -> Add Level. You can change the order in which the data is sorted (First by ID and then by Date).
Brief:
I have a large dataset, inside of which are Individual customer orders by item and quantity. What I'm trying to do is get excel to tell me which order numbers contain exact matches (in terms of items and quantities) to each other. Ideally, I'd like to have a tolerance of say 80% accuracy which I can flex to purpose but I'll take anything to get me off the ground.
Existing Solution:
At the moment, I've used concatenation to pair item with quantity, pivoted and then put the order references as column and concat as rows with quantity as data (sorted by quantity desc) and I'm visually scrolling across/down to find matches and then manually stripping in my main data where necessary. I have about 2,500 columns to check so was hoping I could find a more suitable solution with excel doing the legwork on identification.
Index/matching works at cross referencing a match for the concatenation but of course, the order numbers (which are unique) are different so its not giving me matches ACROSS orders.
Fingers crossed!
EDIT:
Data set with outcomes
As you can see, the bottom order reference has no correlation to the orders above it so is not listed as a match to the orders above but 3 are identical and 1 has a slightly different item but MOSTLY matches.
I am new to couchdb, i have looked at the docs and SO posts but for some reason this simple query is still eluding me.
SELECT TOP 10 * FROM x WHERE DATE BETWEEN startdate AND enddate ORDER BY score
UPDATE: It cannot be done. This is unfortunate since to get this type
of data you have to pull back potentially millions of records (a few
fields) from couch then do either filtering, sorting or limiting
yourself to get the desired results. I am now going back to my
original solution of using _changes to capture and store elsewhere the data i do need to perform that query on.
Here is my updated view (thanks to Dominic):
emit([d.getUTCFullYear(), d.getUTCMonth() + 1, d.getUTCDate(), score], doc.name);
What I need to do is:
Always sort by score descending
Optionally filter by date range (for instance, TODAY only)
Limit by x
Update: Thanks to Dominic I am much closer - but still having an
issue.
?startkey=[2017,1,13,{}]&endkey=[2017,1,10]&descending=true&limit=10&include_docs=true
This brings back documents between the dates sorted by score
However if i want top 10 regardless of date then i only get back top 10 sorted by date (and not score)
For starters, when using complex keys in CouchDB, you can only sort from left to right. This is a common misconception, but read up on Views Collation for a more in-depth explanation. (while you're at it, read the entire Guide to Views as well since you're getting started)
If you want to be able to sort by score, but filter by date only, you can accomplish this by breaking down your timestamp to only show the degree you care about.
function (doc) {
var d = new Date(doc.date)
emit([ d.getUTCFullYear(), d.getUTCMonth() + 1, d.getUTCDate(), score ])
}
You'll end up outputting a more complex key than what you currently have, but you query it like so:
startkey=[2017,1,1]&endkey=[2017,1,1,{}]
This will pick out all the documents on 1-1-2017, and it'll be sorted by score already! (in ascending order, simply swap startkey and endkey to get descending order, no change to the view needed)
As an aside, avoid emitting the entire doc as the value in your view. It is likely more efficient to leverage the include_docs=true parameter, and leaving the value of your emit empty. (please refer to this SO question for more information)
With this exact setup, you'd need separate views in order to query by different precisions. For example, to query by month you just use the year/month and so on.
However, if you are willing/able to sort your scores in your application, you can use a single view to get all the date precision you want. For example:
function (doc) {
var d = new Date(doc.date)
emit([ d.getUTCFullYear(), d.getUTCMonth() + 1, d.getUTCDate(), d.getUTCHour(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds() ])
}
With this view and the group_level parameter, you can get all the scores by year, month, date, hour, etc. As I mentioned, in this case it won't be sorted by score yet, but maybe this opens up other queries to you. (eg: what users participated this month?)
I've been trying to filter the view by second sorted column but so far it doesn't work.
(my underlying view is sorted by first column categorized and sorted by ascending, and the second column is sorted by ascending order as well)
How can i get through this thing? and I don't want to create one more view for this filtering
To filter by multiple keys you need to use a Java Vector with the keys you want to filter by. Here's an example of applying a filter to a sessionScope variable that you then use for the keys property of the view:
var vArray = new java.util.Vector();
vArray.addElement("key1");
vArray.addElement("key2");
sessionScope.put('viewFilter', vArray);
For search function, We have two different ways are there. One is normal search just like OS level.And another is Full index search.
Please follow the below link, U will get better idea,
[Search Query][1]
[1]: http://www-10.lotus.com/ldd/ddwiki.nsf/dx/XPagesViewControlAddFullTextSearch.htm
Here is the case:
I need to display a list of records on a page, and paging is necessary. The question I got is whether a record should be displayed depends on validation result computed in memory, after selected from database.
for example, 50 records for one page:
Select 50 records from database
30 records are left after validation
Solution I have now it get all records from database, do validation and then get valid list of records. Paging is based on this list.
Is there any other good solution for this?
In the optimal case pagination can be divided in two steps. In the first step according to the selecting query a set of rows is selected from a database. All these rows could be displayed. Instead of fetching actual rows just retrieve a list of their identifiers. This list however large can be usually kept in memory. Second step is paging through the list by asking for n-th page of m items. Then only m rows are being completely retrieved from the database using their ids.
Additional step of computation is negating the idea of pagination that is having a list of identifiers of the whole result set.
What I can think of now without seeing the computation is to store results of computation in the database whenever a displaying row is being inserted/updated in the db. Since computation results depend from input parameters then for every row and for every range of input parameters you could have a different result.
This would then make paging possible. Performing the first step of paging should now include precomputed validation results and provide much faster retrieval of the list of row ids.