Assign() to specific indices of vectors, vectors specified by string names-CodePudding

I'm trying to assign values to specific indices of a long list of vectors (in a loop), where each vector is specified by a string name. The naive approach

testVector1 <- c(0, 0, 0)

vectorName <- "testVector1"
indexOfInterest <- 3

assign(x = paste0(vectorName, "[", indexOfInterest, "]"), value = 1)

doesn't work, instead it creates a new vector "testVector1[3]" (the goal was to change the value of testVector1 to c(0, 0, 1)).

I know the problem is solvable by overwriting the whole vector:

temporaryVector <- get(x = vectorName)
temporaryVector[indexOfInterest] <- 1
assign(x = vectorName, value = temporaryVector)

but I was hoping for a more direct approach.

Is there some alternative to assign() that solves this?

Similarly, is there a way to assign values to specific elements of columns in data frames, where both the data frames and columns are specified by string names?

CodePudding user response：

If you must do this you can do it with eval(parse():

valueToAssign  <- 1
stringToParse  <- paste0(
    vectorName, "[", indexOfInterest, "] <- ", valueToAssign
)
eval(parse(text = stringToParse))

testVector1
# [1] 0 0 1

But this is not recommended. Better to put the desired objects in a named list, e.g.:

testVector1 <- c(0, 0, 0)

dat  <- data.frame(a = 1:5, b = 2:6)

l  <- list(
    testVector1 = testVector1,
    dat = dat
)

Then you can assign to them by name or index:


vectorName <- "testVector1"
indexOfInterest <- 3

dfName  <- "dat"
colName  <- "a"
rowNum  <- 3

valueToAssign  <- 1

l[[vectorName]][indexOfInterest]  <- valueToAssign
l[[dfName]][rowNum, colName]  <- valueToAssign

l
# $testVector1
# [1] 0 0 1

# $dat
#   a b
# 1 1 2
# 2 2 3
# 3 1 4
# 4 4 5
# 5 5 6