Reading text using a function like sprintf in R

Question

Suppose I have the following text:

"    7.7597     4.7389     3.0058     0.0013"

I know it's format:

" %9.4f  %9.4f  %9.4f  %9.4f"

I want to extract variables out of it. I want something like sprintf/gettextf function but does does the reverse:

??????(" %9.4f  %9.4f  %9.4f  %9.4f", v1, v2, v3, v4)

How can I do that? (without loading any packages, if possible)

The unreliable method I use right now is:

temp <- as.numeric(unlist(strsplit("    7.7597     4.7389     3.0058     0.0013"," ")))
temp[!is.na(temp)]

Answer 1

I would do:

scan(text="  7.7597     4.7389     3.0058     0.0013")
#Read 4 items
#[1] 7.7597 4.7389 3.0058 0.0013

It correctly reports NAs:

scan(text="   7.7597  NA   4.7389     3.0058     0.0013")
#Read 5 items
#[1] 7.7597     NA 4.7389 3.0058 0.0013

It breaks on malformed input (non-numeric). So you can control it with a tryCatch:

tryCatch(scan(text=" abc  7.7597  4.7389"), error= function(e) cat("Malformed input\n")) 
#Malformed input 

Under the hood

How come that scan gets the floats properly? The function has an argument, what, to set the data type you are scanning for. The default parameter is

scan(...,  what=double())

So it parses pretty well the floats required in the question. Anyway, should you change your needs and looking for different data types, try:

scan(text="  7  4  3  0 ", what=integer())
#Read 4 items
#[1] 7 4 3 0

As usual you can check for data consistency:

tryCatch(scan(text=" 1 2.3", what=integer()), error= function(e) cat("Non-integer value(s) passed!\n")) 
#Non-integer value(s) passed!