R dpylr select_if with multiple conditions

Question

I would like to select all numerical variables, as well as some variables by name. I managed to use select_if to get numeric variables and select to get them by name, but can't combine two into one statement

x = data.table(c(1,2,3),c(10,11,12),c('a','b','c'),c('x','y','z'), c('l', 'm','n'))

I want my result to be:

V1 V2 V4 V5
1 10  x l
2 11  y m
3 12  z n

I tried this, but it does not work.

y = x %>%
select_if(is.numeric, V4, V5)

Answer 1

If we have a data frame x:

x = data.frame(V1=c(1,2,3),V2=c(10,11,12),V3=c('a','b','c'),V4=c('x','y','z'),V5=c('l', 'm','n'), stringsAsFactors=FALSE)
##  V1 V2 V3 V4 V5
##1  1 10  a  x  l
##2  2 11  b  y  m
##3  3 12  c  z  n

where V1and V2in fact numeric, and the remaining columns are not factors, then we can do:

library(dplyr)
y <- x %>% select_if(function(col) is.numeric(col) | 
                                   all(col == .$V4) | 
                                   all(col == .$V5))
##  V1 V2 V4 V5
##1  1 10  x  l
##2  2 11  y  m
##3  3 12  z  n

, , , , . , select_if , , .

- select:

y <- x %>% select(which(sapply(.,class)=="numeric"),V4,V5)
##  V1 V2 V4 V5
##1  1 10  x  l
##2  2 11  y  m
##3  3 12  z  n

, , .

Answer 2

map ( purrr)

library(purrr)
x %>%
     map2(names(x), ~.[is.numeric(.x)|.y != "V3"])  %>%
     Filter(length, .) %>% 
     bind_cols
 #     V1    V2    V4    V5
 #  <dbl> <dbl> <chr> <chr>
 #1     1    10     x     l
 #2     2    11     y     m
 #3     3    12     z     n

@RoyalTS

x %>% 
    imap( ~ .[is.numeric(.x)|.y != "V3"]) %>%
    keep(~length(.x) > 0) %>%
    bind_cols

---

data.table, data.table

x[, sapply(x, is.numeric) | colnames(x) != "V3", with = FALSE]
#   V1 V2 V4 V5
#1:  1 10  x  l
#2:  2 11  y  m
#3:  3 12  z  n

x <- data.table(c(1,2,3),c(10,11,12),c('a','b','c'),c('x','y','z'), 
              c('l', 'm','n')) 

. @nicola , cbind . , , .

Answer 3

data.frame:

x = data.frame(V1=c(1,2,3),V2=c(10,11,12),V3=c('a','b','c'),V4=c('x','y','z'),V5=c('l', 'm','n'))

x %>% select_if(is.numeric) .