[R-sig-Geo] Error running codes

[Enoch Gyamfi Ampadu]

Dear List,

Please I have been running a certain the codes below to read my image,
shapeffile to enable me classify for cover with Random forest. I have
gotten to the point of extracting the raster values and the raster
information. However I keep getting errors. though I have tried different
combination and other codes like readOGR for importing the training
polygon. I will be glad if you could be of help as I am new to using R.

#import clip image of study area

TestImg3 <- brick("C:\\Users\\hp\\Desktop\\Data collection\\Nkandla
Images\\Landsat\\2019\\08052019\\Corrected\\New
Folder\\Image08052019_Clip.tif")

#Assign name of bands
names(TestImg3) <- c(paste0("B", 1:7, coll=""), "B9")
plotRGB(TestImg3, r=4, g=3, b=2, stretch ="lin")

#Import training shapefile
sample <- shapefile("C:/Users/hp/Desktop/Data collection/Nkandla
Images/Landsat/2019/08052019/Corrected/Train08052019_2.shp")

responseCol <- "class"

#(I have tried options of changing "class" to "classname" as reflect actaul
name assigned in ArcMap)

# Overlap the sample polygons on the image (combine the class information
with extracted values).

pixels = data.frame(matrix(vector(), nrow = 0, ncol = length(names(img)) +
1))
for (i in 1:length(unique(sample[[responseCol]]))){
  category <- unique(sample[[responseCol]])[i]
  categorymap <- sample[sample[[responseCol]] == category,]
  dataSet <- extract(img, categorymap)
  dataSet <- dataSet[!unlist(lapply(dataSet, is.null))]
  if(is(sample, "SpatialPointsDataFrame")){
    dataSet <- cbind(dataSet, class = as.numeric(category))
    pixeles <- rbind(pixeles, dataSet)
  }
  if(is(sample, "SpatialPolygonsDataFrame")){
    dataSet <- lapply(dataSet, function(x){cbind(x, class =
as.numeric(rep(category,

 nrow(x))))})
    df <- do.call("rbind", dataSet)
    pixels <- rbind(pixeles, df)
  }

}

THIS IS THE ERROR I GET FROM RUNNING THE ABOVE CODES

> for (i in 1:length(unique(samples[[responseCol]]))){
+   category <- unique(samples[[responseCol]])[i]
+   categorymap <- samples[samples[[responseCol]] == category,]
+   dataSet <- extract(img, categorymap)
+
+   if(is(sample, "SpatialPointsDataFrame")){
+     dataSet <- cbind(dataSet, class = as.numeric(category))
+     pixeles <- rbind(pixeles, dataSet)
+   }
+   if(is(sample, "SpatialPolygonsDataFrame")){
+     dataSet <- lapply(dataSet, function(x){cbind(x, class =
as.numeric(rep(category,
+
  nrow(x))))})
+     df <- do.call("rbind", dataSet)
+     pixels <- rbind(pixeles, df)
+   }
+
+ }
Error in y[i, ] :
  cannot get a slot ("Polygons") from an object of type "NULL"


Please help me out.
Thank you.

Best regards,

Enoch

-- 
*Enoch Gyamfi - Ampadu*

*Geography & Environmental Sciences*

*College of Agriculture, Engineering & Science*

*University of KwaZulu-Natal, Westville Campus*

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*Durban, South Africa **– 4000**.*
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*email: egampadu using gmail.com <egampadu using gmail.com>*


*skype: enoch.ampadu*
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