[R] five multiple plots with ggplot

[Stefano Sofia]

Dear list users,
I would like to have multiple plots in one page with ggplot, in particular five graphs:
in the central plot the snow cover (hs) of two meteorological stations; above wind direction and temperature of one of the two stations and below wind direction and temperature of the other station.

My data frame (df) is like

date hs1 temp1 wind1 wind_dir1 pch_wind_dir1 color_wind_dir1 hs2 temp2 wind2 wind_dir2 pch_wind_dir2 color_wind_dir2
2014-12-27 00:00:00 20 -4.2 6.8 NW 5 "blue" 40 -4.2 6.8 NW 5 "blue"
2014-12-27 00:30:00 22 -4.3 4.3 NNE 5 "cyan" 42 -4.3 4.3 NNE 5 "cyan"
2014-12-27 01:00:00 24 -4.1 5.7 NNW 10 "cyan" 44 -4.1 5.7 NNW 10 "cyan"
2014-12-27 10:00:00 30 -2.6 7.2 NNW 10 "cyan" 44 -3.1 5.7 NNW 10 "cyan"
...

with 48 rows.

The ylim of hs1 and hs2 should be fixed between 0 and 200cm, hs1 colored with blue and the other with red;
wind1 and wind2 should take the pch and color described in each row.

lapply(df, class) gives

$date
[1] "POSIXct" "POSIXt"

$hs1
[1] "numeric"

$temp1
[1] "numeric"

$wind1
[1] "numeric"

and so on.

I have been trying for a long time to do that starting from some examples found in the web, with no success. The example code I started with is

> ggplot(df, aes(date, hs1, ymin=0, ymax=200, colour = "blue")) + scale_colour_identity() + xlim(trunc(df$date[1], "days"), trunc(df$date[48], "days")) + facet_grid(variable ~ ., scales = "free", as.table = FALSE) + theme_bw()
> f1 <- f + geom_step(subset = .(variable =="HS"))

but I always get the following error:
Error in layout_base(data, rows, drop = drop) :
At least one layer must contain all variables used for facetting.

Is the problem due to how date has been specified? I tried both with
> df$date <- strptime(df$olddata, format = "%Y-%m-%d-%H-%M")
and
> df$date <- as.POSIXct(df$olddata, format = "%Y-%m-%d-%H-%M", tz = "")
but the result is the same.

Could somebody help me in that?

Thank you for your attention and your help
Stefano


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