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Questions tagged [mapply]

R function that applies a function to multiple lists or vector arguments.

R function mapply is a multivariate version of sapply. mapply applies FUN argument to the first elements of each argument, the second elements, the third elements, and so on. Arguments are recycled if necessary.

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R data.table apply function to rows using columns as arguments

I have the following data.table x = structure(list(f1 = 1:3, f2 = 3:5), .Names = c("f1", "f2"), row.names = c(NA, -3L), class = c("data.table", "data.frame")) I would like to apply a function to each row of the data.table. The function func.test…
broccoli
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Applying a function to two lists?

To find the row-wise correlation of two matrices X and Y, the output should have a correlation value for row 1 of X and row 1 of Y, ..., hence in total ten values (because there are ten rows): X <- matrix(rnorm(2000), nrow=10) Y <-…
Paul
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Force mapply to return a list?

Suppose I have a function that creates data frames. I'd like to run that function with different input values, and then rbind the results together into one big data frame, as below: CreateDataFrame <- function(type="A", n=10, n.true=8) { …
Adrian
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Apply a function over all combinations of arguments

I would like to be able to apply a function to all combinations of a set of input arguments. I have a working solution (below) but would be surprised if there's not a better / more generic way to do this using, e.g. plyr, but so far have not found…
waferthin
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Avoiding multiple for-loops in R to calculate a matrix

So in the course of generating some fake data to answer a map question, I found myself writing the following: # Generate some fake data lat <- seq(-90, 90, by = 5) lon <- seq(-180, 180, by = 10) phi <- matrix(0, nrow = length(lat), ncol =…
Mike Wise
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R: apply a function to every element of two variables respectively

I have a function with two variables x and y: fun1 <- function(x,y) { z <- x+y return(z) } The function work fine by itself: fun1(15,20) But when I try to use it with two vectors for x and y with an apply function I do not get the correct…
adam.888
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Vectorize() vs apply()

The Vectorize() and the apply() functions in R can often be used to accomplish the same goal. I usually prefer vectorizing a function for readability reasons, because the main calling function is related to the task at hand while sapply is not. It…
andrew
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R data.table column names not working within a function

I am trying to use a data.table within a function, and I am trying to understand why my code is failing. I have a data.table as follows: DT <- data.table(my_name=c("A","B","C","D","E","F"),my_id=c(2,2,3,3,4,4)) > DT my_name my_id 1: A …
Sam
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Non-standard evaluation of subset argument with mapply in R

I can not use the subset argument of xtabs or aggregate (or any function I tested, including ftable and lm) with mapply. The following calls fail with the subset argument, but they work without: mapply(FUN = xtabs, formula = list(~ wool, …
Thomas
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quantmod::chart_Series and mapply gives error with chart parameters

How do I use MoreArgs properly with chart_Series? p.txt s,n ABBV,AbbVie BMY,Bristol LLY,EliLily MRK,Merck PFE,Pfizer sof.r # R --silent --vanilla <…
AG1
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mapply for all arguments' combinations [R]

Consider this toy function that receives 3 arguments: toy <- function(x, y, z){ paste(x, y, z) } For each argument I have a number of values (not necessarily the same number for each argument) and I want to apply the toy function to the…
elikesprogramming
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Why does data.table get copied when returned from Map

I understood that data.table is not copied when returned from a function. However, in this particular case it does get copied. Can one explain why? dt1 <- data.table(a=1) dt2 <- data.table(b=1) dt3 <- data.table(c=1) address(dt1); address(dt2);…
imsc
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Row-wise sort then concatenate across specific columns of data frame

(Related question that does not include sorting. It's easy to just use paste when you don't need to sort.) I have a less-than-ideally-structured table with character columns that are generic "item1","item2" etc. I would like to create a new…
C8H10N4O2
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mapply basics? - how to create a matrix from two vectors and a function

I am trying create a data.frame from which to create a graph. I have a function and two vectors that I want to use as the two inputs. This is a bit simplified, but basically all I have is: relGPA <- seq(-1.5,1.5,.2) avgGPA <- c(-2,0,2) f <-…
Sam Swift
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Apply different functions to different columns programmatically in data.table R

I need to programmatically apply different functions to different columns and group by, using data.table. If the columns and functions were known, I would do like this: library(data.table) DT = data.table(id = rep(letters[1:3], each=3), …
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