R：基于多列中的值选择行

Question

I've a data frame which have many columns with common prefix "_B" e,g '_B1', '_B2',...'_Bn'. So that I can grab the column names by:

allB <- c(grep( "_B" , names( my.df ),value = TRUE ) )

I wish to select the rows for which each of these _B* columns passes a single condition like values >= some_cutoff

Can someone tell how to do that, my efforts with 'all()' and 'any()' failed

set.seed(12345)     
my.df <- data.frame(a = round(rnorm(10,5),1), m_b1= round(rnorm(10,4),1),m_b2=round(rnorm(10,4),1))
allB <- c(grep( "_b" , names( my.df ),value = TRUE ) )
> my.df
     a m_b1 m_b2
1  5.6  3.9  4.8
2  5.7  5.8  5.5
3  4.9  4.4  3.4
4  4.5  4.5  2.4
5  5.6  3.2  2.4
6  3.2  4.8  5.8
7  5.6  3.1  3.5
8  4.7  3.7  4.6
9  4.7  5.1  4.6
10 4.1  4.3  3.8

I wish to select rows for which every m_b1 and m_b2 column is >= 4.0

Answer 1

We could use filter_at from dplyr , and specify all_vars (if all the values in the row meets the condition. If it is any of the value in the row, it would be any_vars )

library(dplyr)
my.df %>%
   filter_at(allB, all_vars(. >= some_cutoff))

data

some_cutoff <- 3
my.df <- structure(list(`_B1` = c(1, 1, 9, 4, 10), `_B2` = c(2, 3, 12, 
 6, 12), V3 = c(3, 6, 13, 10, 13), V4 = c(4, 5, 16, 13, 18)), .Names = c("_B1", 
 "_B2", "V3", "V4"), row.names = c(NA, -5L), class = "data.frame")

allB <- grep( "_B" , names( my.df ),value = TRUE ) 

Answer 2

In base R :

some_cutoff = 4
selectedCols <- my.df[grep("_b", names(my.df), fixed = T)]
selectedRows <- selectedCols[apply(selectedCols, 1, 
                                   function(x) all(x>=some_cutoff)), ]

selectedRows
#   m_b1 m_b2
# 2  5.8  5.5
# 6  4.8  5.8
# 9  5.1  4.6

grep() is used to get the indices of columns with the pattern of interest, which is then used to subset my.df . apply() iterates over rows when the second argument, MARGIN = 1 . The anonymous function returns TRUE if all() the entries match the condition. This logical vector is then used to subset selectedCols .