I wanted to ask if the following scenario is somehow possible to happen.
I have an Nsmutablearray and i have in it 5 objects. I load the Nsmutablearray on an uitableview. I want to insert a new object at the top of the other five objects but also move down all the previously inserted objects down by one. let me give you an example
0 one
1 two
2 three
3 four
4 five
i want to result like this after the new object inserted on the top
0 six
1 one
2 two
3 three
4 four
5 five
Any help appreciated.
- (void)insertObject:(id)anObject atIndex:(NSUInteger)index
This method of NSMutableArray is what you are looking for.
If index is already occupied, the objects at index and beyond are shifted by adding 1 to their indices to make room.
The method you are looking for is: - [NSMutableArray insertObject:atIndex:].
In your example, the index would be 0.
Related
I have a 7 dimensional jagged array that essentially is just a collection of decimal numbers. I need to go through the array and add up all the decimals that have certain values in certain columns. For example;
(A)(B)(..)(..)(..)(..)(..)
Where .. is the entire size of the dimention. For the above case I can simply use a bunch of nested for loops because I know that A and B are at the start of the array. But how can I deal with this if the dimention in which A and B are located is randomised. Eg.
(..)(A)(..)(..)(B)(..)(..)
Or
(..)(..)(..)(..)(..)(A)(B)
Or
(..)(..)(A)(..)(..)(..)(B)
Etc.
I thought about have a select case for the locations of A and B but this leads to hundreds (if not thousands) of lines of repeated code, and it feels like bad practice.
Any suggestions?
Edit #1
This is difficult to explain so I'm going to use a much more simple example. Instead of 7 dimentions let's say it's 2 dimentions (each with a length of 4). And instead of A and B let's say it's just A. I wish to add the following elements:
(A)(0)
(A)(1)
(A)(2)
(A)(3)
(0)(A)
(1)(A)
(2)(A)
(3)(A)
As you can see this is every element where A is in either of the dimentions (A is a real number, in this case either 0, 1, 2, or 3). Now in my case there's the need for both A and B to be in one of the dimentions and the requirement that A is always before B. But since there's 7 dimentions there's so many possible locations of A and B that writing code to each scenario is not ideal (also I'd like to extend it to C, D, etc.)
There is an inconsistency with dataframes that I cant explain. In the following, I'm not looking for a workaround (already found one) but an explanation of what is going on under the hood and how it explains the output.
One of my colleagues which I talked into using python and pandas, has a dataframe "data" with 12,000 rows.
"data" has a column "length" that contains numbers from 0 to 20. she wants to divided the dateframe into groups by length range: 0 to 9 in group 1, 9 to 14 in group 2, 15 and more in group 3. her solution was to add another column, "group", and fill it with the appropriate values. she wrote the following code:
data['group'] = np.nan
mask = data['length'] < 10;
data['group'][mask] = 1;
mask2 = (data['length'] > 9) & (data['phraseLength'] < 15);
data['group'][mask2] = 2;
mask3 = data['length'] > 14;
data['group'][mask3] = 3;
This code is not good, of course. the reason it is not good is because you dont know in run time whether data['group'][mask3], for example, will be a view and thus actually change the dataframe, or it will be a copy and thus the dataframe would remain unchanged. It took me quit sometime to explain it to her, since she argued correctly that she is doing an assignment, not a selection, so the operation should always return a view.
But that was not the strange part. the part the even I couldn't understand is this:
After performing this set of operation, we verified that the assignment took place in two different ways:
By typing data in the console and examining the dataframe summary. It told us we had a few thousand of null values. The number of null values was the same as the size of mask3 so we assumed the last assignment was made on a copy and not on a view.
By typing data.group.value_counts(). That returned 3 values: 1,2 and 3 (surprise) we then typed data.group.value_counts.sum() and it summed up to 12,000!
So by method 2, the group column contained no null values and all the values we wanted it to have. But by method 1 - it didnt!
Can anyone explain this?
see docs here.
You dont' want to set values this way for exactly the reason you pointed; since you don't know if its a view, you don't know that you are actually changing the data. 0.13 will raise/warn that you are attempting to do this, but easiest/best to just access like:
data.loc[mask3,'group'] = 3
which will guarantee you inplace setitem
I'm writing an app where a group of people must mark each other. So I have a "Users" array like this:
0: paul
1: sally
2: james
3: bananaman
The first item Paul is marked (out of ten) by the other three, and then the second item Sally is marked by the other three (index 2, 3, 0) and so on, to create a "Results" array like this one:
0: paul, sally, 5
1: paul, james, 7
2: paul, bananaman, 9
3: sally, james, 4
I'm keeping track of the current 'scorer' and 'being_scored' integers as a new score gets added, which looks like this:
scorer = 1, being_scored = 0
scorer = 2, being_scored = 0
scorer = 3, being_scored = 0
scorer = 0, being_scored = 1
scorer = 2, being_scored = 1
However the group can stop scoring at any point, and a different group session could be loaded, which was also partially scored.
My question is how can I generate the 'scorer' and 'being_scored' values based only on the results [array count].
Presumably it's the [results count] divided by [users count] - 1, with the resulting whole number 'being_scored' and the remainder is the 'scorer'.
But my brain is utterly fried after a long week and this doesn't seem to be working.
Any help much appreciated
Mike.
Ignoring your added comment that the "Results" array is multi-dimensional and simply contains structs/objects with three fields/properties: scored, scorer, score; then surely you just go to the last element of "Results" (at index [Results count]-1), select the scored and scorer and move on to the next in your sequence - which you presumably have logic for already in the case the loop was not interrupted (something like "if last scorer precedes being_scored [treating the array as a circular buffer by using modulo arithmetic] then advanced being_scored and init scorer else advance scorer").
But then that sounds rather obvious, but you did say you brain was fried...
Not Ignoring your added comment implies you have a two-dimensional array of scores which you are filling up in some pattern? If this is a pre-allocated array of some number type then if you init it with an invalid score (negative maybe?) you scan the array following your pattern looking for the first invalid score and restart from there. If it is a dynamic single dimensional array of single dimensional arrays then the count of the outer one tells you the being_scored, and the count of the last inner one tells you the scorer...
But that sounds rather obvious as well...
Maybe some sleep? Then reframe the question if you're still stuck? Or maybe this bear of little brain missed the point entirely and somebody else will figure out your question for you.
[This is more a comment than an answer, but its too long for a comment, sorry.]
I have 3 NSArrays with:
item: amount
A: 1
B: 2
C: 3
A: 2
E: 1
F: 6
C: 5
D: 1
F: 3
After "combining" these into one, I need:
A: 3
B: 2
C: 8
D: 1
E: 1
F: 9
Do I first combine all the arrays into one and then sum and remove the duplicates?
You could use an NSCountedSet. I'm not clear on the structure of the data in your arrays, but by assuming that your B: 2 means that you have two B's in the array, then something like this would work:
NSCountedSet *set = [NSCountedSet setWithCapacity:[array1 count]+[array2 count]+[array3 count]];
[set addObjectsFromArray:array1];
[set addObjectsFromArray:array2];
[set addObjectsFromArray:array3];
// Test it out!
NSUInteger countForC = [set countForObject:objC];
// countForC == 8
Instead of using a NSArray you could try using a NSMutableDictionary where the key is inherent in the objects structure. That will allow you to iterate through each of your arrays of letters and counts then query for the value with the key, get the value and add to the value, then continue processing.
One possibility would be to use:
Use predicates to extract like sets of data (by item) into separate arrays. See Collection predicates guide
Key Value Coding to sum the value field of each of the resulting arrays (by item). See KVO collection operators.
Pop the results in whatever structure you like (NSArray or NSDictionary).
There may be performance considerations to explore. Alternatively, iterate the array, pulling out matching items in a separate NSDictionary (keyed on item) and summing as you go.
I have 2 NSArray's that are holding values...
For example NSArray 1 has values 1 2 4 in it
and NSArray 2 has values 1 2 4 5 6 in it.
How can I write code to compare these 2 arrays to get the following information...
Count the values that are the same (so in this case 3) and count the values that are not the same (in this case 2).
I am simply populating the arrays like this:
NSString *s = #"1,2,4";
NSArray *numbers = [s componentsSeparatedByString:#","];
where *s is actually getting the text from a UITextField. If sorting mattering in comparing can you show me code to sort to make sure the user doesnt put the numbers in order?
If you are fine with sets instead of arrays, you can use NSMutableSet instead of NSArray. NSMutableSet has nice methods like intersectSet: and minusSet:
I would probably use the following method of the NSArray class:
enumerateObjectsUsingBlock.
and code the block testing for membership in the other array with the method:
indexOfObjectIdenticalTo.
If this isn't clear to you let me know.