How to initialize a vector with fixed length in R ??
For example, I want a vector of characters with length of 10??
To create a vector of specified data type and length in R we make use of function vector().
Setting length of the object in R Programming Here we are going to set the length of the vector in R Programming, for this we will use length() function. Parameters: x: vector or object.
There are two methods to create a vector with repeated values in R but both of them have different approaches, first one is by repeating each element of the vector and the second repeats the elements by a specified number of times. Both of these methods use rep function to create the vectors.
length() function gets or sets the length of a vector (list) or other objects. When resets a list or matrix, if the list is shortened, extra values will be discarded, if the list is lengthened, NAs (or nul ) is added to the list. length() function can be used for all R objects.
It's good that you ask because pre-allocating long vectors before for-loops that will be assigning results to long objects are made more efficient by not needing to successively lengthen vectors.
?vector X <- vector(mode="character", length=10)
This will give you empty strings which get printed as two adjacent double quotes, but be aware that there are no double-quote characters in the values themselves. That's just a side-effect of how print.default
displays the values. They can be indexed by location. The number of characters will not be restricted, so if you were expecting to get 10 character element you will be disappointed.
> X[5] <- "character element in 5th position" > X [1] "" "" [3] "" "" [5] "character element in 5th position" "" [7] "" "" [9] "" "" > nchar(X) [1] 0 0 0 0 33 0 0 0 0 0 > length(X) [1] 10
Technically, lists are "vectors" in R, so this is a recommended (even necessary) practice for constructing lists with for-loops:
obj <- list( length(inp_vec) ) for ( i in seq_along(inp_vec) ){ obj[[i]] <- some_func( inp_vec[i] ) }
@Tom reminds us that the default for 'mode' is logical and that R has a fairly rich set of automatic coercion methods, although I find his suggestion vector(,10)
to be less clear than would be logical(10)
which is its equivalent.
If you want to initialize a vector with numeric values other than zero, use rep
n <- 10
v <- rep(0.05, n)
v
which will give you:
[1] 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05
The initialization method easiest to remember is
vec = vector(,10); #the same as "vec = vector(length = 10);"
The values of vec are: "[1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE" (logical mode) by default.
But after setting a character value, like
vec[2] = 'abc'
vec becomes: "FALSE" "abc" "FALSE" "FALSE" "FALSE" "FALSE" "FALSE" "FALSE" "FALSE" "FALSE"", which is of the character mode.
Just for the sake of completeness you can just take the wanted data type and add brackets with the number of elements like so:
x <- character(10)
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