Question: I would like to create plot which looks like this:

![enter image description here][1]

[1]: https://imgur.com/O3m6P8Z.jpg

So the plot would include 5 different data sets, where each data set would be line in different color as shown on the figure.

Right now my code looks like this:

qqunif = function(p, BH=T, MAIN = " ", SUB=" ")
{
nn = length(p)
xx = -log10((1:nn)/(nn+1))
plot( xx, -sort(log10(p)),
main = MAIN, sub= SUB, cex.sub=1.3,
xlab=expression(Expected~~-log[10](italic(p))),
ylab=expression(Observed~~-log[10](italic(p))),
cex.lab=1.0,mgp=c(2,1,0))
abline(0,1,col='red')
if(BH) ## BH = include Benjamini Hochberg FDR
{

abline(-log10(0.05),1, col='black',lty=1)
text(0.5,1.9 , "FDR=0.05", col = "gray60",srt=30, cex=1)
abline(-log10(0.10),1, col='black',lty=1)
text(0.5, 1.6, "FDR=0.10", col = "gray60",srt=30, cex=1)
abline(-log10(0.25),1, col='black',lty=1)
text(0.5, 1.2, "FDR=0.25", col = "gray60",srt=30, cex=1)
#legend('topleft', c("FDR = 0.05","FDR = 0.10","FDR = 0.25"),
#col=c('black','black','black'),lty=c(1,1,1), cex=0.8)
if (BF)
{
abline(h=-log10(0.05/nn), col='black') ## bonferroni
}
}
}

My datasets look like this:

dat1
MARKER META_pval
rs10001545 0.8868792
rs1000281 0.04879765
rs10004027 0.7946071
rs10006766 0.8806172
rs100087 0.2386829
rs10009948 0.8135963
rs1001160 0.3008881
rs1001464 0.2580996
...

dat2
MARKER META_pval
rs100087 0.2386829
rs1001160 0.3008881
rs1001581 0.2703533
rs10028441 0.9162814
rs1003061 0.9763203
rs1006985 0.3121185
rs1010984 0.9283012
rs1012775 0.8503905
...

dat3
MARKER META_pval
rs1001581 0.2703533
rs100192 0.7959347
rs10028441 0.9162814
rs10036674 0.6278337
rs10037276 0.6222389
rs10038816 0.5864842
rs1006985 0.3121185
rs10077458 0.5905193
...

dat4
MARKER META_pval
rs10140304 0.8737664
rs10156094 0.7813031
rs10203656 0.5107122
rs10211771 0.3846588
rs10224066 0.7827652
rs10228441 0.5194636
rs10235405 0.5694455
...

META_pval is my pvalue column, and you would normally run my code like: p_run=dat$META_pval, qqunif(p_run). This would create regular QQplot, the same like on the figure above but just with one line. So I could run my code on say dat1, like p_run1=dat1$META_pval, qqunif(p_run1). But how to run it for all 4 dat files and get QQ plot with 4 lines?
Any idea on this would be appreciated, also alternative ggplot solutions.

Answer: I think you can first plot the "base" plot, then plot line for each dataset.
Hope this works. :-)

```
# Function to fetch qq values
get_qqdf = function(p) {
nn = length(p)
xx = -log10((1:nn) / (nn + 1))
df = data.frame("x" = xx, "y" = -sort(log10(p)))
return(df)
}

# Get limits of x-axis and y-axis
qq_lim = as.data.frame(rbind(
sapply(get_qqdf(dat1$META_pval), max),
sapply(get_qqdf(dat2$META_pval), max),
sapply(get_qqdf(dat3$META_pval), max),
sapply(get_qqdf(dat4$META_pval), max)
))
qq_xlim = max(qq_lim$x)
qq_ylim = max(qq_lim$y)

# Plot the base figure
plot(
NULL,
main = "",
sub = "" ,
cex.sub = 1.3,
xlim = c(0, qq_xlim),
ylim = c(0, qq_ylim),
xlab = expression(Expected ~ ~ -log[10](italic(p))),
ylab = expression(Observed ~ ~ -log[10](italic(p))),
cex.lab = 1.0,
mgp = c(2, 1, 0)
)
abline(0, 1, col = 'red')
abline(-log10(0.05), 1, col = 'black', lty = 1)
text(0.5,
1.9 ,
"FDR=0.05",
col = "gray60",
srt = 30,
cex = 1)
abline(-log10(0.10), 1, col = 'black', lty = 1)
text(0.5,
1.6,
"FDR=0.10",
col = "gray60",
srt = 30,
cex = 1)
abline(-log10(0.25), 1, col = 'black', lty = 1)
text(0.5,
1.2,
"FDR=0.25",
col = "gray60",
srt = 30,
cex = 1)

# Plot each dataset
lines(get_qqdf(dat1$META_pval), col = "#DD3429")
lines(get_qqdf(dat2$META_pval), col = "#41ACCB")
lines(get_qqdf(dat3$META_pval), col = "#1E9173")
lines(get_qqdf(dat4$META_pval), col = "#EE876C")
```