If you combine all of the df's into a list, e.g.
dfn <- paste0("df", 1:20)
df <- lapply(dfn, get)
names(df) <- dfn
and if "target" is the day you want in the same date/time format as the day
variable in the data frames:
sapply(df, function(x) x[x$day==target, "tmax"])
will return a named vector of the tmax values.
-------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77840-4352
-----Original Message-----
From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Stefano Sofia
Sent: Thursday, May 14, 2015 9:23 AM
To: r-help@r-project.org
Subject: [R] create a vector from several data frames
Dear r-users,
suppose that I have 20 data frames df1, df2, ..., df20 (one for each different
location) with the same column names and column types (the first column
contains a date, the others are numeric) like
day tmax tmin
2015-05-10 20 10
2015-05-11 21 12
2015-05-12 17 9
2015-05-13 24 13
2015-05-14 25 18
I need to create a vector "tmax_all" of length 20 with the tmax referred to a
particular day (let's say 2015-05-14).
I would first build a new data frame
tmax_df <- Reduce(function(x, y) merge(x, y, by="day"), list(df1[ , c("day",
"tmax")], df2[ , c("day", "tmax")], ..., df20[ , c("day", "tmax")]))
and then select the row of tmax_df where day is the day I want to.
Is there an easiest way? Is it possible to create straightforward this vector
without passing through the merge of all the data frames?
Thank you for your help
Stefano
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