[R] How to create gridded data

[lily li]

Now I have new question about this post. If the grid coordinates in DF1 are
not complete, i.e. there are missing coordinates, how to fill these with
-99 in the exported DF2? Thanks.

On Thu, Nov 15, 2018 at 10:57 PM David L Carlson <dcarlson using tamu.edu> wrote:

> It would depend on the format of the gridded data. Assuming it is a data
> frame like DF2 in my earlier answer, you just reverse the steps:
>
> > DF2
>      110.5 111 111.5 112
> 46     6.1 4.5   7.8 5.5
> 45.5   3.2 5.0   1.8 2.0
>
> > DF3 <- data.frame(as.table(as.matrix(DF2)))
>   Var1  Var2 Freq
> 1   46 110.5  6.1
> 2 45.5 110.5  3.2
> 3   46   111  4.5
> 4 45.5   111  5.0
> 5   46 111.5  7.8
> 6 45.5 111.5  1.8
> 7   46   112  5.5
> 8 45.5   112  2.0
>
> But the latitude and longitude get converted to factors and we lose the
> column names:
>
> > DF3 <- data.frame(as.table(as.matrix(DF2)))
> > colnames(DF3) <- c("latitude", "longitude", "Precip")
> > DF3$latitude <- as.numeric(as.character(DF3$latitude))
> > DF3$longitude <- as.numeric(as.character(DF3$longitude))
>
> ----------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77843-4352
>
> From: lily li <chocold12 using gmail.com>
> Sent: Tuesday, November 13, 2018 10:50 PM
> To: David L Carlson <dcarlson using tamu.edu>
> Cc: Sarah Goslee <sarah.goslee using gmail.com>; R mailing list <
> r-help using r-project.org>
> Subject: Re: [R] How to create gridded data
>
> Thanks, Sarah's answer helps the question. Now how to change the gridded
> data back to DF1 format? I don't know how to name the format, thanks.
>
> On Tue, Nov 13, 2018 at 10:56 PM David L Carlson <mailto:dcarlson using tamu.edu>
> wrote:
> Sarah's answer is probably better depending on what you want to do with
> the resulting data, but here's a way to go from your original DF1 to DF2:
>
> > DF1 <- structure(list(latitude = c(45.5, 45.5, 45.5, 45.5, 46, 46, 46,
> +         46), longitude = c(110.5, 111, 111.5, 112, 110.5, 111, 111.5,
> +         112), Precip = c(3.2, 5, 1.8, 2, 6.1, 4.5, 7.8, 5.5)),
> +         class = "data.frame", row.names = c(NA, -8L))
> >
> # Convert to table with xtabs()
> > DF2 <- xtabs(Precip~latitude+longitude, DF1)
> >
>
> # Reverse the order of the latitudes
> > DF2 <- DF2[rev(rownames(DF2)), ]
> > DF2
>         longitude
> latitude 110.5 111 111.5 112
>     46     6.1 4.5   7.8 5.5
>     45.5   3.2 5.0   1.8 2.0
>
> # Convert to a data frame
> > DF2 <- as.data.frame.matrix(DF2)
> > DF2
>      110.5 111 111.5 112
> 46     6.1 4.5   7.8 5.5
> 45.5   3.2 5.0   1.8 2.0
>
> ----------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77843-4352
>
>
> -----Original Message-----
> From: R-help <mailto:r-help-bounces using r-project.org> On Behalf Of Sarah
> Goslee
> Sent: Tuesday, November 13, 2018 8:16 AM
> To: lily li <mailto:chocold12 using gmail.com>
> Cc: r-help <mailto:r-help using r-project.org>
> Subject: Re: [R] How to create gridded data
>
> If you want an actual spatial dataset, the best place to ask is R-sig-geo
>
> R has substantial capabilities for dealing with gridded spatial data,
> including in the sp, raster, and sf packages.
>
> Here's one approach, creating a SpatialGridDataFrame, which can be
> exported in any standard raster format using the rgdal package.
>
> DF2 <- DF1
> coordinates(DF2) <- ~longitude + latitude
> gridded(DF2) <- TRUE
> fullgrid(DF2) <- TRUE
>
> I recommend Roger Bivand's excellent book:
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__www.springer.com_us_book_9781461476177&d=DwMFaQ&c=ODFT-G5SujMiGrKuoJJjVg&r=veMGHMCNZShld-KX-bIj4jRE_tP9ojUvB_Lqp0ieSdk&m=vZqNKoDe8N1TzBzeK12g2oa0cBS8VD6NDCs-hUhvt5o&s=B73PwZQrdKUmM1ML2Y5zjaEz7xqkHlzBDCrhluogK2U&e=
>
> and there are abundant web tutorials.
>
> Sarah
> On Tue, Nov 13, 2018 at 2:22 AM lily li <mailto:chocold12 using gmail.com>
> wrote:
> >
> > Hi R users,
> >
> > I have a question about manipulating data. For example, I have DF1 as the
> > following, how to transform it to a gridded dataset DF2? In DF2, each
> value
> > Precip is an attribute of the corresponding grid cell. So DF2 is like a
> > spatial surface, and can be imported to ArcGIS. Thanks for your help.
> >
> > DF1
> > latitude   longitude   Precip
> > 45.5           110.5         3.2
> > 45.5           111            5.0
> > 45.5           111.5         1.8
> > 45.5           112            2.0
> > 46              110.5         6.1
> > 46              111            4.5
> > 46              111.5         7.8
> > 46              112            5.5
> > ...
> >
> >
> > DF2
> > 6.1   4.5   7.8   5.5
> > 3.2   5.0   1.8   2.0
> > ...
> >
>
>
> --
> Sarah Goslee (she/her)
>
> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.numberwright.com&d=DwMFaQ&c=ODFT-G5SujMiGrKuoJJjVg&r=veMGHMCNZShld-KX-bIj4jRE_tP9ojUvB_Lqp0ieSdk&m=vZqNKoDe8N1TzBzeK12g2oa0cBS8VD6NDCs-hUhvt5o&s=qSosThG59aeSFYzVFf1e-YQGbuBKVbvgVi1z9nFm884&e=
>
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