R-language throws error (list) object cannot be coerced to type ‘double‘ when we try to convert a list of string or other type values to a numeric vector.

To correctly coerce a list, you should unlist it first and then convert into numeric vector.

a <- structure(list(`X$Days` = c("10", "38", "66", "101", "129", "185", "283","374")), .Names = "X$Days")

There are different types of objects in R which could be coerced during computations. Some of these objects are –

"symbol"a variable name
"pairlist"a pairlist object (mainly internal)
"closure"a function
"environment"an environment
"promise"an object used to implement lazy evaluation
"language"an R language construct
"special"an internal function that does not evaluate its arguments
"builtin"an internal function that evaluates its arguments
"char"a ‘scalar’ string object (internal only) ***
"logical"a vector containing logical values
"integer"a vector containing integer values
"double"a vector containing real values
"complex"a vector containing complex values
"character"a vector containing character values
"..."the special variable length argument ***
"any"a special type that matches all types: there are no objects of this type
"expression"an expression object
"list"a list
"bytecode"byte code (internal only) ***
"externalptr"an external pointer object
"weakref"a weak reference object
"raw"a vector containing bytes
"S4"an S4 object which is not a simple object

Some other examples of coercion are –

> labs <- paste(c("X","Y"), 1:10, sep="")
c("X1", "Y2", "X3", "Y4", "X5", "Y6", "X7", "Y8", "X9", "Y10")

Here we used paste() function which takes an arbitrary number of arguments and concatenates them one by one into character strings. So, they are coerced into characters.

According to R manuals

A list whose components conform to the restrictions of a data frame may be coerced into a data frame using the function as.data.frame()

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I am Akash Mittal, an overall computer scientist. If you want to guest post, need help in your projects, want to advertise, Feel free to contact me at [email protected]

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