A common algorithm in functional languages that applies an operation to each member of a sequence, from left to right.
Questions tagged [foldleft]
103 questions
3
votes
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foldLeft with Double
I' am trying to use foldLeft to calculate the sum of all Double in a Vector.
Using reduce works fine but I just can't figure out why it doesn't with foldLeft
scala> val prices = Vector(20.0, 9.5,8.4,9.1)
prices:…
ccheneson
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How to perform unknown functions on list of lists in Haskell with foldl/foldr/recursion?
I want to write something using foldl/foldr or recursion, what performs tasks one after another in the previously performed "state" with the next Job's function. It needs to work with any type of given variable/function.
The time is irrelevant now,…
donaldtheduckkk00
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2
votes
1 answer
Using foldl, write a function that converts a list of integers to an integer number?
I'm trying to write a function dec2int that converts a list of integers to an integer number. My only constraint is that I must use foldl.
The type signature for the function is:
dec2int :: [Int] -> Int
The function should work in this way:
Input: …
Dave B
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2
votes
2 answers
How to convert tail recursive method to more Scala-like function?
In my code, I very often need to process a list by performing operations on an internal model. For each processed element, the model is returned and then a 'new' model is used for the next element of the list.
Usually, I implement this by using a…
John Doe
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2
votes
1 answer
Scala new Map column from integer and string columns
Problem Statement:
I have a dataframe with four columns: service (String), show (String), country_1 (Integer), & country_2 (Integer). My objective is to produce a dataframe that consists of just two columns: service (String) & information…
corgi123
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2
votes
2 answers
Arguments not needed when using foldl in haskell?
What I don't get is how it is possible to use foldl in this way in haskell. I do not understand how the argument ( in this case list) is carried over implicitly:
addAll :: [Int] -> Int
addAll = foldl (+) 0
-- This is how I could write foldl to…
Nilo
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2
votes
1 answer
How to sum number of Ints and Number of Floats within a List - Scala
I need to calculate the number of integers and floats i have in a Map which is like Map[String, List[(Int, String, Float)]]
The data comes from reading a file - the data inside for example looks kinda like (however there is a few more Routes):…
CycleNew
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2
votes
1 answer
How to get a size of a tree-like custom object
I am trying to figure out how to get the size (num of "levels") of a custom tree-like data structure defined this way:
case class PrefixTreeImpl[K, +V](value: Option[V], prefixTree: Map[K, PrefixTree[K, V]]) extends PrefixTree[K, V]
As you can see…
Burn_jacks
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2
votes
2 answers
Concatenate List of Strings, adding a separator in between using foldl Haskell
I have a function that is meant to combine strings in a list, adding a separator in between each and outputting a single string using foldl. Here is what I have and some expected behavior of the function -- It isn't working and I'm unsure why.
-- |…
Scott Myers
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2
votes
2 answers
Foldl on a list of functions in Haskell
I'm trying to write a function, pipe that takes a list of mathematical functions where pipe [f1,...,fn] x should return f1(f2(...(fn x)))
I've set it up such that:
pipe :: [(a -> a)] -> (a -> a)
pipe fs = foldLeft f base fs
where
f a x = …
Scott Myers
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2
votes
2 answers
foldLeft sum values with BigDecimal.ZERO start value
I have requirement where I want sum values of all employee salaries in list
employeeList.foldLeft(java.math.BigDecimal.ZERO) { (accSal,emp) => accSal + getSalary(emp,designation,yearsOfExp) }
Here for each employee I want to call a function…
mprad
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2
votes
1 answer
How to convert a fold left operator ":/" into the foldLeft function in scala?
The following code sums the values of the two maps into a single map.
val merged = (map1 /: map2) { case (map, (k,v)) =>
map + ( k -> (v + map.getOrElse(k, 0)) )
}
However I am unsuccessful in converting it using the foldLeft()()…
Dev A
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votes
4 answers
Implementing Haskell's `take` function using `foldl`
Implementing Haskell's take and drop functions using foldl.
Any suggestions on how to implement take and drop functions using foldl ??
take x ls = foldl ???
drop x ls = foldl ???
i've tried these but it's showing errors:
myFunc :: Int -> [a] ->…
amir ahmed
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2
votes
2 answers
Spark Scala FoldLeft resulting in StackOverflow when run in the cluster
Im using the following code in order to re-shape a dataframe using its rows for this reshaping.
The dataframe contains the date of when a product changes its ID, but in order to join it with a huge other dataframe containing the transactions, I need…
I want badges
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2
votes
1 answer
How to break early when foldLeft over simple List?
This is a simplified version of my problem, I want to stop the fold return the value after the if condition is met in the fold where a.size == 7.
class test1 {
def test(a : List[Int]): Int = {
val list = a.foldLeft(if(a.size == 7) 1000 else…
Gioan Nguyen
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