Remove space between bars within a grid - r

Question

I want to move bars that are within one grid closer to save space. Is there a way to do that? The code I used just change the bar width and does not change the spacing. I am aware that bindwidth no longer work in geom_bar as I referred to these problems:
Adding space between bars in ggplot2
Increase space between bars in ggplot
This is the data
dput(grp1)
structure(list(Rot = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("2-year",
"3-year", "4-year"), class = "factor"), Rot.Herb = structure(c(3L,
4L, 13L, 14L, 5L, 6L, 9L, 10L, 15L, 16L, 1L, 2L, 7L, 8L, 11L,
12L, 17L, 18L), .Label = c("A4-conv", "A4-low", "C2-conv", "C2-low",
"C3-conv", "C3-low", "C4-conv", "C4-low", "O3-conv", "O3-low",
"O4-conv", "O4-low", "S2-conv", "S2-low", "S3-conv", "S3-low",
"S4-conv", "S4-low"), class = "factor"), Rot.trt = structure(c(2L,
2L, 7L, 7L, 3L, 3L, 5L, 5L, 8L, 8L, 1L, 1L, 4L, 4L, 6L, 6L, 9L,
9L), .Label = c("A4", "C2", "C3", "C4", "O3", "O4", "S2", "S3",
"S4"), class = "factor"), Crop = structure(c(2L, 2L, 4L, 4L,
2L, 2L, 3L, 3L, 4L, 4L, 1L, 1L, 2L, 2L, 3L, 3L, 4L, 4L), .Label = c("alfalfa",
"corn", "oat", "soybean"), class = "factor"), Year = c(2014L,
2014L, 2014L, 2014L, 2014L, 2014L, 2014L, 2014L, 2014L, 2014L,
2014L, 2014L, 2014L, 2014L, 2014L, 2014L, 2014L, 2014L), Herb.trt = structure(c(1L,
2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 1L,
2L), .Label = c("conv", "low"), class = "factor"), variable = structure(c(1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
1L), .Label = "kg.ha", class = "factor"), N = c(4, 4, 4, 4, 4,
4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4), value = c(0.43168573275,
16.22463846275, 0.554446363, 25.89844593075, 13.882743364, 84.1922080725,
84.2625, 105.7375, 0.8350420895, 106.7464386085, 127.8875, 65.3875,
1.964170084, 29.46524929925, 249.7625, 333.125, 0.535560112,
28.757014893), sd = c(0.528135488290589, 20.3216237207314, 0.8810357408252,
40.4576156325903, 27.3195114207629, 71.6424882235524, 22.6948736869511,
40.9587266851237, 0.931926987921512, 108.45555847826, 89.1035387905553,
25.141843442092, 2.20017281317418, 24.1072626208021, 93.2983509589889,
85.0439543216722, 0.48339034731648, 33.2628789566726), se = c(0.264067744145294,
10.1608118603657, 0.4405178704126, 20.2288078162951, 13.6597557103815,
35.8212441117762, 11.3474368434756, 20.4793633425619, 0.465963493960756,
54.2277792391299, 44.5517693952777, 12.570921721046, 1.10008640658709,
12.0536313104011, 46.6491754794945, 42.5219771608361, 0.24169517365824,
16.6314394783363), ci = c(0.840381416699796, 32.3362381637038,
1.40192446910603, 64.3770946952626, 43.4714390915815, 113.999185974188,
36.112608456959, 65.1744742040986, 1.48290379975249, 172.576995683309,
141.783613905853, 40.0062833851536, 3.50096592013592, 38.3600344290379,
148.458496149248, 135.323909108861, 0.76918191241357, 52.928663119381
)), .Names = c("Rot", "Rot.Herb", "Rot.trt", "Crop", "Year",
"Herb.trt", "variable", "N", "value", "sd", "se", "ci"), row.names = c(NA,
-18L), class = "data.frame")
This is the code
ggplot(grp1, aes(x=Rot.Herb, y=value, fill=factor(Herb.trt)))+
geom_bar(stat="identity", position=position_dodge(.), width=.5)+
scale_fill_brewer(palette = "Dark2")+
theme_bw() +
theme(panel.grid.major=element_blank()) +
facet_grid(~Crop, scales = "free_x", space="free_x")+
theme(legend.title=element_blank(),legend.text=element_text(size=20),legend.position="top")+
geom_errorbar(aes(ymin=value-se, ymax=value+se), size=0.75, width=.25,position=position_dodge(.5))+
xlab("Treatment") +
theme(axis.title = element_text(size=24,face="bold", vjust=4)) +
ylab("2014 total weed biomass (Kg/ha)\n") +
theme(axis.title = element_text(size=24,face="bold", vjust=2), axis.text.y = element_text(size=20, color="black"))+
theme(strip.text.x = element_text(colour = "black", size = 15), strip.background = element_rect(fill = "white"), axis.text.x = element_blank(), axis.ticks.x = element_blank())
And graph
What I want is a graph with bar width of 0.5 and no spacing between bars in the same grid. Thank you for all the input.

Answer 1

I think you want width = 0.5 while keeping the bars touching because you don't want the absolute width to change (width = 0.5 changes the relative width). This might be closer to what you are asking for.
ggplot(grp1, aes(x=Rot.Herb, y=value, fill=factor(Herb.trt)))+
geom_bar(stat="identity", position = "dodge", width=1)+
scale_x_discrete(expand=c(0.2,0))+
scale_fill_brewer(palette = "Dark2")+
theme_bw() +
theme(panel.grid.major=element_blank()) +
facet_grid(~Crop, scales = "free_x", space="free_x")+
theme(legend.title=element_blank(),legend.text=element_text(size=20),legend.position="top")+
geom_errorbar(aes(ymin=value-se, ymax=value+se), size=0.75, width=.25,position=position_dodge(0.5))+
xlab("Treatment") +
theme(axis.title = element_text(size=24,face="bold", vjust=4)) +
ylab("2014 total weed biomass (Kg/ha)\n") +
theme(axis.title = element_text(size=24,face="bold", vjust=2), axis.text.y = element_text(size=20, color="black"))+
theme(strip.text.x = element_text(colour = "black", size = 15), strip.background = element_rect(fill = "white"), axis.text.x = element_blank(), axis.ticks.x = element_blank())
Basically I changed the width = 1 as suggested by #Gregor, which causes the bars to touch, but added an extra option scale_x_discrete(expand=c(0.2,0)) to add spaces between the bars and the sides of the plot. This in effect adjusts the absolute width of the bars while keeping them touching. The first number gives the multiplicative constant used to expand the range, while the second gives the additive.
You can experiment with the two values in expand = to get what you want.
Also see this related question: ggplot geom_boxplot: reduce space between x-axis categories