[R] data frame returned from sapply but vector expected

[PIKAL Petr]

Hallo all

 

I found a strange problem for coding if part of list is NULL. 

In this case, sapply result is ***list of data frames*** but if there is no
NULL leaf, the result is ***list of vectors***. 

I tried simplify option but it did not help me neither I found anything in
help page. 

 

The code is part of bigger project where I fill list by reading in data and
if it fails, the leaf is set to NULL. Then the the boxplot is created simply
by

boxplot(sapply(mylist2, "[", "b")) and the user is asked to select if values
should be rbinded or not.

 

Is it possible to perform some *apply without getting data frame as result
in case NULL leaf?

 

Here is an example (without boxplot)

 

df1 <- data.frame(a=rnorm(5), b=runif(5), c=rlnorm(5))

df2 <- data.frame(a=rnorm(5), b=runif(5), c=rlnorm(5))

mylist1 <- list(df1,df2, df3)

mylist2 <- list(NULL,df2, df3)

> str(sapply(mylist1, "[", "b"))

List of 3

$ b: num [1:5] 0.387 0.69 0.876 0.836 0.819

$ b: num [1:5] 0.01733 0.46055 0.19421 0.11609 0.00789

$ b: num [1:5] 0.593 0.478 0.299 0.185 0.847

> str(sapply(mylist2, "[", "b"))

List of 3

$ : NULL

$ :'data.frame':       5 obs. of  1 variable:

  ..$ b: num [1:5] 0.01733 0.46055 0.19421 0.11609 0.00789

$ :'data.frame':       5 obs. of  1 variable:

  ..$ b: num [1:5] 0.593 0.478 0.299 0.185 0.847

 

S pozdravem | Best Regards

RNDr. Petr PIKAL
Vedoucí Výzkumu a vývoje | Research Manager

PRECHEZA a.s.
nábř. Dr. Edvarda Beneše 1170/24 | 750 02 Přerov | Czech Republic
Tel: +420 581 252 256 | GSM: +420 724 008 364
 <mailto:petr.pikal using precheza.cz> petr.pikal using precheza.cz |
<https://www.precheza.cz/> www.precheza.cz

Osobní údaje: Informace o zpracování a ochraně osobních údajů obchodních
partnerů PRECHEZA a.s. jsou zveřejněny na:
<https://www.precheza.cz/zasady-ochrany-osobnich-udaju/>
https://www.precheza.cz/zasady-ochrany-osobnich-udaju/ | Information about
processing and protection of business partner's personal data are available
on website:
<https://www.precheza.cz/en/personal-data-protection-principles/>
https://www.precheza.cz/en/personal-data-protection-principles/

Důvěrnost: Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné
a podléhají tomuto právně závaznému prohlášení o vyloučení odpovědnosti:
<https://www.precheza.cz/01-dovetek/> https://www.precheza.cz/01-dovetek/ |
This email and any documents attached to it may be confidential and are
subject to the legally binding disclaimer:
<https://www.precheza.cz/en/01-disclaimer/>
https://www.precheza.cz/en/01-disclaimer/