loop "functions" and "for loops" through list of dataframes

Question

Hy. I'm working with shapefiles in R. I wrote a script which processes one of my shapefiles. Therefore I wrote mutliple functions and for loops. After processing the shapefile it will be written to another folder. Now i need to apply this to all my shapefiles. Is there an easy way to do this? I'm new to R.

What I've got sofar: Script for one shapefile, which looks like this: Upload the file and set time format:

setwd("")
shape=ReadOGR(dsn=", layer= "Trip_2")
shape$Zeit= as.POSIXct(strptime(shape$Zeit_txt, format= "%d.%m.%Y%H:%M:%S", tz="GMT"), tz="GMT")

First extractions: make Wegtyp NA if Count is not 1

shape$wegtyp[shape$Count != 1] = NA
shape$name_wegty[shape$Count != 1] = NA
shape$OBJECTVAL[shape$Count != 1] = NA
shape$name_weg_1[shape$Count != 1] = NA

First Function:

calculateDistancesWGS = function(long, lat){
  distWGS = long
  distWGS = NA
  for (i in 1:(length(lat)-1)){
    distWGS[i+1] = distCosine( c(long[i+1], lat[i+1]), c(long[i], lat[i]))
  }
  return(distWGS)
}

shape$distanceWGS = calculateDistancesWGS(shape$longitude, shape$latitude)

several more function follow

extract file as shapefile:

 writeOGR(shape, dsn= "", layer= "Trip_03", driver= "ESRI Shapefile" )

Now I need to do this with all my shapefiles and save them with different names. I'm able to import several shapefiles to R creating a list of dataframes like this:

 setwd("")
list_shp <-        list.files(path="", pattern="*.shp", full.names = TRUE,
                       recursive = TRUE, include.dirs = FALSE)
shapes <- lapply(list_shp, function(x) {readOGR(dsn=x,     layer=ogrListLayers(x))})

But when it gets to applying the timeformat and the functions i could not figure out what to do.

Here's a short example of my data:

d1= data.frame(longitude=(10.42206), latitude= (46.60109), Wegtyp= (1),     Zeit_txt= 14.50)
d2= data.frame (longitude= (10.42207), latitude= (46.60108), Wegtyp= 2, Zeit_txt= (14.55))

Any help would be highly appreciated

Frank · Accepted Answer · 2014-12-03 18:00:42Z

1

You can just lapply a function that does the command you wanted, like the following:

addTime <- function(shape) { 
  shape$Zeit= as.POSIXct(strptime(shape$Zeit_txt, format= "%d.%m.%Y%H:%M:%S", tz="GMT"), tz="GMT")
  return(shape)
}
shapes <- lapply(shapes, addTime)

answered Dec 3, 2014 at 18:00

Frank

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8 Comments

daverous Over a year ago

Thanks a lot, works perfectly and I now unterstand what it does. Could you also give me an example how to do this for the first function? Do I have to make a function around a function here? Thanks again for your help

Frank Over a year ago

Since it's a list of data.frames, you'll want to wrap the part that adds the column to the data.frame in a function, and lapply as above. For example: addDistance <- function(shape) shape$distanceWGS = calculateDistancesWGS(shape$longitude, shape$latitude); return(shape)

daverous Over a year ago

Works. Exactly the solution i was looking for. Thanks a lot.

daverous Over a year ago

Mhhm, another question. I figured out how to apply your suggestions to all my functions. However I'm now stuck at writing each dataframe as a new shapefile. I'd like the name to be shape_1, shape_2 and so on. I use writeOGR to save as shapefile. Here's my code for one shapefile: writeOGR(shapes, dsn= "", layer= "shape_1", driver= "ESRI Shapefile" ) Since I'm new to programming I don't see a good way to do this. Could you help me out with this?

Frank Over a year ago

Are you trying to write each of the dataframes in the list shapes as its own shapefile? For this you'd want to make a vector of the names, e.g., c("shape_1", "shape_2") (or look at the paste function) and use a for loop or mapply to iterate over the elements of the list.

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