How to filter rows with NA based on multiple conditions

Question

How to drop rows with NA (missing values) based on multiple conditions in group column?

Here is the dummy data:

a <- data.frame(c('b1', 'b2', 'b3', 'b4'),
                c(NA, 1.5, 0.5, 1),
                c(0.4, NA, 0.3, NA),
                c(0.5, NA, NA,2),
                c(-0.5, -2.5, -0.2,NA),
                c(NA, NA, -0.4,NA),
                c(-0.5, NA, -0.4,NA),
                stringsAsFactors = FALSE)

colnames(a) <- c('id', 'group1_1', 'group1_2', 'group1_3', 'group2_1', 'group2_2', 'group2_3')
rownames(a) <- a$id

a_subset <- a[, 2:7]
a_subset

#    group1_1 group1_2 group1_3 group2_1 group2_2 group2_3
# b1       NA      0.4      0.5     -0.5       NA     -0.5
# b2      1.5       NA       NA     -2.5       NA       NA
# b3      0.5      0.3       NA     -0.2     -0.4     -0.4
# b4      1.0       NA      2.0       NA       NA       NA

As you can see from above dataframe, group_1 and group_2 contains some missing values, and each group has triplicates.

Expected output:

#    group1_1 group1_2 group1_3 group2_1 group2_2 group2_3
# b1       NA      0.4      0.5     -0.5       NA     -0.5
# b3      0.5      0.3       NA     -0.2     -0.4     -0.4
# b4      1.0       NA      2.0       NA       NA       NA

From above you can see if 1 group contains at least 2 values it will not be removed.

Is it possible with dplyr approach?

Answer 1

tidyverse

library(tidyverse)

a_subset %>% 
  filter(
    rowSums(!is.na(across(starts_with("group1_")))) >= 2 | 
      rowSums(!is.na(across(starts_with("group2_")))) >= 2)

#>    group1_1 group1_2 group1_3 group2_1 group2_2 group2_3
#> b1       NA      0.4      0.5     -0.5       NA     -0.5
#> b3      0.5      0.3       NA     -0.2     -0.4     -0.4
#> b4      1.0       NA      2.0       NA       NA       NA

data

a_subset <- data.frame(
   row.names = c("b1", "b2", "b3", "b4"),
    group1_1 = c(NA, 1.5, 0.5, 1),
    group1_2 = c(0.4, NA, 0.3, NA),
    group1_3 = c(0.5, NA, NA, 2),
    group2_1 = c(-0.5, -2.5, -0.2, NA),
    group2_2 = c(NA, NA, -0.4, NA),
    group2_3 = c(-0.5, NA, -0.4, NA)
)