# For loop to execute a process and save the data set using specific name

Hi,

I have an original raster file (.tif format) and I want to blur it with a gaussian filter using different sigma parameters which are increasing with step 0.05 (i.e., sigma = 0.2, then sigma = 0.25, etc). Finally, I'd like like those newly created rasters to be saved with their original name + the sigma value I used to create them (e.g., my original raster's name is evi.tif and my goal is the exported raster to be named as evi02.tif, evi025.tif etc).
I have done this for a single raster but I have to repeat the process 15 more times for a range of sigma 0.2 to 0.9 (step 0.05). Can anyone help me? Here is the code for a single raster.

evi = raster("path/evi.tif")

gf <- focalWeight(evi, 0.2, "Gauss")
r_gf <- focal(evi, w = gf)

writeRaster(r_gf, "path/evi02.tif")


Here is the input raster:

new("RasterLayer", file = new(".RasterFile", name = "C:\\Users\\nikos\\OneDrive\\Desktop\\tst\\evi.tif",
datanotation = "FLT8S", byteorder = "little", nodatavalue = -Inf,
NAchanged = FALSE, nbands = 1L, bandorder = "BIL", offset = 0L,
toptobottom = TRUE, blockrows = 256L, blockcols = 256L, driver = "gdal",
open = FALSE), data = new(".SingleLayerData", values = logical(0),
offset = 0, gain = 1, inmemory = FALSE, fromdisk = TRUE,
isfactor = FALSE, attributes = list(), haveminmax = FALSE,
min = Inf, max = -Inf, band = 1L, unit = "", names = "evi"),
legend = new(".RasterLegend", type = character(0), values = logical(0),
color = logical(0), names = logical(0), colortable = logical(0)),
title = character(0), extent = new("Extent", xmin = 983600,
xmax = 1033100, ymin = 976000, ymax = 1028800), rotated = FALSE,
rotation = new(".Rotation", geotrans = numeric(0), transfun = function ()
NULL), ncols = 495L, nrows = 528L, crs = new("CRS", projargs = "+proj=lcc +lat_0=28.62510126 +lon_0=77 +lat_1=28.375 +lat_2=28.875 +x_0=1000000 +y_0=1000000 +datum=WGS84 +units=m +no_defs"),
history = list(), z = list())


Thank you

Hello,

you can write a custom function which takes the \sigma value as input and does what you want. Then, you can use a for-loop or (better) something like lapply() to accomplish your needs:

evi <- raster("path/evi.tif")

blurr_it <- function(raster_obj, sigma_val){
# define the objects you did in the request
gf <- focalWeight(raster_obj, sigma_val, "Gauss")
r_gf <- focal(raster_obj, w = gf)
# custom file name
# e.g. for sigma_val = 0.2 : path/evi_20.tif
writeRaster(r_gf, paste0("path/evi_",100 * sigma_val,".tif"))
}

# apply the function to a sequence, ranging from 0.2 to 0.9 (15 steps, including 0.2)
lapply(seq.default(from = 0.2, by = 0.05, length.out = 15),
blurr_it, raster_obj = evi)


Hope this helps you

1 Like

Yes, works perfectly. Many thanks

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