I am trying to generate random numbers but only certain numbers. I know to generate a random number between 0 and 10 you'd use:
arc4random_uniform(11)
But what if I wanted to generate a random number between a selection of, say 3, 5, 8, and 10?
Vacawama is right and should be given credit.
a little more thought.
Chose what number you want and put them into an array. then use the index of the array to get the
[3, 5, 8, 10]
array index starts at zero so; [0: 3, 1: 5, 2: 8, 3: 10].
using "4" within the arc4random will let you choose between 0-3.
Related
I have a timestamp for every record in the data set.
I heard about time based spiting but don't know anything about it.
Normal cross-validation
You have a set of data points:
data_points = [2, 4, 5, 8, 6, 9]
Then, if you do a 2-fold split, your data points will get randomly assigned to 2 different groups.
For example:
split_1 = [2, 5, 9]
split_2 = [3, 8, 6]
However, this assumes that there is no need to keep the order of your data points.
You can train your model with split_1 and test it with split_2.
Time based splitting
However, this assumption isn't always correct for time series prediction.
For example, given the same data points:
data_points = [2, 4, 5, 8, 6, 9]
It can be that they are arranged by time.
You could then have a model that to predict the next number, it looks back 3 time steps. (e.g. to predict the number after 9, it will have [8, 6, 9] as input. Meaning that the order of which the data points appear is important. Because of that, in order to test your model, you cannot randomly split your data points. The order in which they appear needs to be kept.
So if you do a 2-fold split, you could get the following splits:
split_1 = [2, 4, 5, 8]
split_2 = [5, 8, 6, 9]
Implementation
There is an implementation of time-based cross-validation from Sklearn: the TimeSeriesSplit.
I'm looking to list and count unique values from multiple cells. The practical application is to list and count the scenes in a movie that a particular character appears in.
I'm using the following array formula to list the scenes from the data table:
=ArrayFormula(TEXTJOIN(", ",TRUE,IF($B$11:$B$64=E13,$A$11:$A$64,"")))
It will returns something like this (these are the scene numbers):
2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4
But I want it to return:
2,3,4
Then to count the unique values I used the following formula:
COUNTUNIQUE(SPLIT(F13,", ",0))
But the problem here is that it returns "1" even when the array formula correctly returns no value (i.e. the character didn't appear in any scene)
Here is the Google Sheet so you can see things in context:
https://docs.google.com/spreadsheets/d/1dwrORFJ508duRP1no7258dqLemujkOjpvA3XmolqtsU/edit?usp=sharing
Any help will be greatly appreciated!
F11:
=ARRAYFORMULA(TEXTJOIN(",",1,UNIQUE(IF(E11=B$11:B,A$11:A,))))
=COUNT(SPLIT(F11,","))
Use UNIQUE() to find unique values before joining them
SPLIT parameter 1 can't be empty, which gives a #VALUE error,Which is counted as 1 with COUNTUNIQUE.Use IFERROR to mask it.(Since we already have unique values, COUNT is simpler)
I have a number of fruit baskets, all of them have a random amount of apples and they have different properties.
arrayOfBaskets = [
["basketId": 1, "typeOfPesticidesUsed": 1, "fromCountry":1, "numberOfApples": 5],
["basketId": 2, "typeOfPesticidesUsed": 1, "fromCountry":1, "numberOfApples": 6],
["basketId": 3, "typeOfPesticidesUsed": 2, "fromCountry":1, "numberOfApples": 3],
["basketId": 4, "typeOfPesticidesUsed": 2, "fromCountry":1, "numberOfApples": 7],
["basketId": 5, "typeOfPesticidesUsed": 1, "fromCountry":2, "numberOfApples": 8],
["basketId": 6, "typeOfPesticidesUsed": 1, "fromCountry":2, "numberOfApples": 4],
["basketId": 7, "typeOfPesticidesUsed": 2, "fromCountry":2, "numberOfApples": 9],
["basketId": 8, "typeOfPesticidesUsed": 2, "fromCountry":2, "numberOfApples": 5]
]
in this case, how do I formulate an algorithm of sorts to output into an array like so:
uniquePairingOfBasketProperties = [
["typeOfPesticidesUsed": 1, "fromCountry":1],
["typeOfPesticidesUsed": 2, "fromCountry":1],
["typeOfPesticidesUsed": 1, "fromCountry":2],
["typeOfPesticidesUsed": 2, "fromCountry":2]
]
my main point is so that I can get my UITableView to know how many rows it should have. Which in this case is 4 instead of total number of baskets.
Huh? You have an array of dictionaries. You want to divide those dictionaries into "buckets" where each bucket has a unique combination of pesticide type and country of origin?
Assuming that's the case, how about this:
let kNumberOfCountries = 2
uniqueValue = basket["typeOfPesticidesUsed"] * kNumberOfCountries +
basket["fromCountry"]
uniqueValue will jump in large steps based on the type of pesticide, and then change by 1s based on the country of origin. (think of a rectangular grid where the country number starts at 1 on the left and increases to the right, and the pesticide number starts at 1 at the top and increases as you go down. The unique value number is 1 at the top left square, counts up to the right, then wraps around to the next row and keeps counting up by 1s.
You can then group your table view based on uniqueVaue.
If you want to know how many unique parings you have, create an empty set of integers. Loop through your array of baskets. Calculate the uniqueValue for that basket, and add it to the set of uniqueValues (sets only have one entry for each value.) Once you are done looping, the number of entries in the set is the number of unique pairings you have. If you use an NSCountedSet, you can even get the count of the number of baskets with each pairing. (I don't know if Swift has a native counted set collection. It didn't last time I checked.)
EDIT:
It looks like Swift does NOT have a native counted set collection (at least not yet.) There is, however, at least one open source Swift counted set (aka a bag) on Github
I am trying to get a random number between 3, 4, and 26-29.
I have tried rand(3, 4, 26..29), but was unsuccessful. Theses are product id numbers that I am trying to assign object to randomly.
Any help is beneficially and welcomed.
There may be a nicer syntax, but this should do the trick :
([3,4]+(26..29).to_a).sample
I have some data that needs to be summed but I would like to set the maximum value at 20, so sum the values but the greatest number that would be returned is 20.
For example, let's say I have three columns labeled A, B, and C. If in row one, the values are 5, 5, 5, the sum should be 15. But if they are 10, 10, 10, I would like the "sum" to show 20 instead of 30.
I have been playing around the the GT() function, but I would not like to create a new column just for comparisons. I would like it all to be in one cell. What would be a simple way of doing this?
=MIN(20, SUM(A1:C1))
maybe? That's what I'd use in Excel...