[R] Get data from a list of data frames (Stefano Sofia)

[Jorgen Harmse]

Following Bert Gunter's suggestion, I wonder why the data are in separate frames (with hard-coded values) in the first place. You could put them in a text file and call read.table. If you provide a header and put a meaningful station name at the start of each data row then rownames of your data frame will be meaningful.

Regards,
Jorgen Harmse.

From: R-help <r-help-bounces using r-project.org> on behalf of r-help-request using r-project.org <r-help-request using r-project.org>
Date: Friday, 16December, 2022 at 05:00
To: r-help using r-project.org <r-help using r-project.org>
Subject: [EXTERNAL] R-help Digest, Vol 238, Issue 16

Message: 1
Date: Thu, 15 Dec 2022 13:52:35 +0000
From: Stefano Sofia <stefano.sofia using regione.marche.it>
To: "r-help using R-project.org" <r-help using R-project.org>
Subject: [R] Get data from a list of data frames
Message-ID: <fe9017cbd4ba49328e150061032068a7 using regione.marche.it>
Content-Type: text/plain; charset="utf-8"

Dear R-list users,

I have a list of n data frames built as follows:


Station1 <- data.frame(sensor = c("thermometer", "raingauge", "snowgauge", "anemometer"), code = c(2583, 1478, 3178, NA))
Station2 <- data.frame(sensor = c("thermometer", "raingauge", "snowgauge", "anemometer"), code = c(2584, 1479, 3179, 4453))
....

Total <- list("Station1"=Station1, "Station2"=Station2, ...)

I would need to have a vector with the sensor codes of the thermometers of some stations, let's say of Station1, Station2 and Station5 (i.e. c(2583, 2584, 2587)).
I tried with lapply, but I have not been able to get what I need.
Could you please help me?

Thank you

Stefano



         (oo)
--oOO--( )--OOo--------------------------------------
Stefano Sofia PhD
Civil Protection - Marche Region - Italy
Meteo Section
Snow Section
Via del Colle Ameno 5
60126 Torrette di Ancona, Ancona (AN)
Uff: +39 071 806 7743
E-mail: stefano.sofia using regione.marche.it
---Oo---------oO----------------------------------------

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Message: 4
Date: Thu, 15 Dec 2022 09:31:51 -0800
From: Bert Gunter <bgunter.4567 using gmail.com>
To: Gerrit Eichner <gerrit.eichner using math.uni-giessen.de>,
        stefano.sofia using regione.marche.it
Cc: r-help using r-project.org
Subject: Re: [R] Get data from a list of data frames
Message-ID:
        <CAGxFJbTgwQ2Nop0bjCzcT7Ri6FhDmOrXiXv+o2-2m_-sqZ6H_w using mail.gmail.com>
Content-Type: text/plain; charset="utf-8"

Well, just for giggles, Gerrit's solution can be easily vectorized (i.e. no
apply()-type stuff needed) IFF the structure of all the data frames are
identical so that rbind() works:

d <-do.call('rbind',Total[select.stat]) ## one data frame to combine them
all ;-)
d[d$sensor == 'thermometer','code']

Whether this is better, worse, or unneeded, I cannot say.

Cheers,
Bert



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