CODEWITHSUNDEEP
rdata-conversion
Heikki
Heikki

Reputation: 2254

Extract nonnegative number or alternatively return negative number from a vector of strings

I need to extract a nonnegative number from a string or return negative number if a number was not extracted.

For extracting the number I found the following way:

> grep("^[0-9.]+","1234.1234alsk",value=TRUE)
[1] "1234.1234alsk"

If the given string is not a number, then empty string is returned:

> grep("^[0-9.]+","",value=TRUE)
character(0)

Now I would like to replace the empty string with some proxy number, like 0 or -1 using the following kind of function:

> sub("^$","-1","")
[1] "-1"

However, If I apply that function to an empty string of character(0) I do not get the desired result:

> sub("^$","-1",grep("^[0-9.]+","",value=TRUE))
character(0)

The problem is that grep returns character(0) and not "". Then because sub works differently with character(0) and "", I do not get the desired value "-1" but unchanged character(0). As a result those values will be dropped in the following query:

> v <- c("0","","1","2")
> as.numeric(sub("^$","-1",grep("^[0-9.]+",v,value=TRUE)))
[1] 0 1 2

How could I do the above kind of conversion using one-liner?

Upvotes: 0

Views: 86

Answers (1)

Heikki
Heikki

Reputation: 2254

By preloading stringr, I found the following one liner to fetch the first occurrence of a number:

> library(stringr)
> x <- c("","1","1.23","1.23a","-123")
> as.vector(ifelse(is.na(str_match(x,"^[0-9.]+")),"-1",str_match(x,"^[0-9.]+")))
[1] "-1"   "1"    "1.23" "1.23" "-1"

and as a result, I can do the following conversions as one-liners:

> as.numeric(as.vector(ifelse(is.na(str_match(x,"^[0-9.]+")),"-1",str_match(x,"^[0-9.]+"))))
[1] -1.00  1.00  1.23  1.23 -1.00
> all.is.numeric(as.numeric(as.vector(ifelse(is.na(str_match(x,"^[0-9.]+")),"-1",str_match(x,"^[0-9.]+")))))
[1] TRUE

The conversion is stored in a column field, therefore, the one-liner requirement is a necessity here.

Upvotes: 1

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