metagen - plotStudySizes: order by year and not alphabetical

-----Original Message-----
From: antoviral at gmail.com
Sent: Sat, 30 May 2015 14:01:28 +0200
To: r-help at r-project.org
Subject: [R] metagen - plotStudySizes: order by year and not alphabetical

HI everybody.
I'm using the package 'metagen' to plot sample size in meta-analysis.
The plot function of the package reorders the studies by alphabetcial
order.
However, I would like to have the studies listed by year.
How can I force the plotting function to order the study by the variable
'year' rather than by the first initial of the variable 'reference'?

Thank you in advance,
Antonello

Here my sample code:


### the data

df <- structure(list(reference = structure(c(3L, 6L, 9L, 2L, 8L, 5L,
7L, 10L, 4L, 1L), .Label = c("Bellani et al. 2012             ",
"Bocco et al. 2004              ", "Costa 1998          ",
"Dalla Volta et al. 2011           ", "Manzanere et al. 2006
",
"McEnty et al. 2001             ", "Ossian et al. 2006                ",
"Simone et al. 2004               ", "Tanter et al. 2002         ",
"Zimmian et al. 2006              "), class = "factor"), size = c(20,
288, 70, 138, 475, 191, 918, 80, 508, 205), year = c(1998, 2001,
2002, 2004, 2004, 2006, 2006, 2006, 2011, 2012)), .Names = c("reference",
"size", "year"), class = "data.frame", row.names = c(NA, -10L
))

### a quick look at the data

head(df)
str(df)

### the library

library(metagen); library(ggplot2)

### the plot

p1 <- plotStudySizes(df)
p1 <- p1 + ggtitle("Studies with Cross-sectional estimates")
p1

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