How to loop a function in a text file? - r

Question

I have a function that I want to use it but the inputs are from a text file.
Here is the Fun:
myfun <- function(latitude,longitude) {
column =latitude*5
row =longitude*3
return(c(column, row))
}
Now I have a text file with information for my function.
cor=read.table("C:\\Data\\AMS.txt", sep="")
head(cor)
V1 V2 V3 V4 V5 V6
1 lat 13 lon 2 Site: As
2 lat 14 lon 3 Site: Ad
Output needed for instance:
lat lon column row site
13 2 ? ? As
I can do this manually but as I have many, it would be better to let R do it. Any hints are appreciated

Answer 1

Try:
data.frame(lat=DF$V2, lon=DF$V4, column=DF$V2*5, row=DF$V4*3, site=DF$V6)
No need for cleaning.
Data
DF <- read.table(text=" V1 V2 V3 V4 V5 V6
1 lat 13 lon 2 Site: As
2 lat 14 lon 3 Site: Ad", header=T)
> DF1 <- data.frame(lat=DF$V2, lon=DF$V4, column=DF$V2*5, row=DF$V4*3, site=DF$V6)
> DF1
lat lon column row site
1 13 2 65 6 As
2 14 3 70 9 Ad

Answer 2

Unless you need to use a function I would use a vectorised solution. First, I'd tidy up your data frame:
cor <- read.table("C:\\Data\\AMS.txt", sep="") # note <- not =
require("dplyr")
cor <- select(cor, -V1)
cor <- select(cor, -V3)
cor <- select(cor, -V5)
colnames(cor) <- c("lat", "long", "site")
Then I'd simply create a new variable for column and row:
cor$column <- cor$lat * 5
cor$row <- cor$long * 3
Yielding:
cor
# lat long site column row
# 1 13 2 As 65 6
# 2 14 3 Ad 70 9
EDIT: Based on your comments and edited post you clearly have a more complex function, which I've attempted to vectorise below. The output is for a vector of 5 items for each of columns and row, so hopefully that's your expected behaviour.
kR = 6371.228 # recommend constants start with 'k'
kC = 25.067525
kNc = 1383
kNl = 586
kR0 = (kNc - 1) / 2
kS0 = (kNl - 1) / 2
kDeg2rad_cte = pi/180
cor$lamda <- cor$lon * kDeg2rad_cte
cor$phi <- cor$lat * kDeg2rad_cte
column <- round(kR0 + (kR / kC) %*% cor$lamda * cos(pi / 6)) + 1
row <- 586 - round(kS0 - (kR / kC) %*% sin(cor$phi) / cos(pi / 6))
column <- seq(min(column), max(column), by=1)
row <- seq(min(row), max(row), by=1)
column
# [1] 700 701 702 703 704
row
# [1] 360 361 362 363 364