[R] apply loop - using/providing a data frame to loop over

[Daniel Malter]

Hi,

I want to extract individual names from a single string that contains all
names. My problem is not the extraction itself, but the looping over the
extraction start and end points, which I try to realize with apply.

#Say, I have a string with names.
authors=c("Schleyer T, Spallek H, Butler BS, Subramanian S, Weiss D,
Poythress ML, Rattanathikun P, Mueller G")

#Since I only want the surname and the initial of the first name, I create
respective indices
starts=c(1, 13, 24, 35, 50, 59, 73, 90)
ends=c(10, 21, 31, 47, 56, 69, 87, 98)

#Now I can extract the names, e.g. the third one, with
substr(authors,start=starts[3],stop=ends[3])

#So far so good, but I want to loop over all indices using apply
#For that I wrote a function g, that takes "a" as the author string, and
"data" as the start and end points for extraction
g=function(a,data){substr(a,data[,1],data[,2])}

#If provided with a specific row of the data frame, g works
g(authors,data.frame(starts,ends)[3,])

#If I try to loop g through the rows of the starts/ends data frame, it does
not work.
apply(data.frame(starts,ends),1,g,a=authors)

#Interestingly, if the data frame to loop over is just a vector, it works
also (e.g. for extracting just the first initial)
g=function(e,a){substr(a,e,e)}
apply(data.frame(ends),1,g,a=authors)

So the problem probably lies in correctly supplying "apply" with the data
frame. I would greatly appreciate your help.

Daniel

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