Problem using rowwise() to count the number of NA's in each row of a dataframe

2

I'm having trouble using rowwise() to count the number of NAs in each row. My minimal example:

df <- data.frame(Q1 = c(rep(1, 1), rep(NA, 9)),
                 Q2 = c(rep(2, 2), rep(NA, 8)),
                 Q3 = c(rep(3, 3), rep(NA, 7))
)
df
   Q1 Q2 Q3
1   1  2  3
2  NA  2  3
3  NA NA  3
4  NA NA NA
5  NA NA NA
6  NA NA NA
7  NA NA NA
8  NA NA NA
9  NA NA NA
10 NA NA NA

I would like to create a new column that counts the number of NAs in each row. I can do this very simply by writing

 df$Count_NA <- rowSums(is.na(df))
 df
   Q1 Q2 Q3 Count_NA
1   1  2  3        0
2  NA  2  3        1
3  NA NA  3        2
4  NA NA NA        3
5  NA NA NA        3
6  NA NA NA        3
7  NA NA NA        3
8  NA NA NA        3
9  NA NA NA        3
10 NA NA NA        3

But if I try and do this via dplyr using rowwise(), I get the wrong answer - the column Count_NA has the same number in each row:

df %>%
   rowwise() %>%
   mutate(Count_NA = sum(is.na(.)))
# A tibble: 10 x 4
# Rowwise: 
      Q1    Q2    Q3 Count_NA
   <dbl> <dbl> <dbl>    <int>
 1     1     2     3       24
 2    NA     2     3       24
 3    NA    NA     3       24
 4    NA    NA    NA       24
 5    NA    NA    NA       24
 6    NA    NA    NA       24
 7    NA    NA    NA       24
 8    NA    NA    NA       24
 9    NA    NA    NA       24
10    NA    NA    NA       24

what am I doing wrong, and how do i fix this?

Many thanks in advance

Thomas Philips

r dplyr rowwise

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edited Apr 18 at 16:50

Waldi

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asked Apr 18 at 16:27

Thomas PhilipsThomas Philips

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2

• Does this answer your question? Count NAs per row in dataframe – TarJae Apr 18 at 16:58
• Probable duplicate: Understanding rowwise and c_across – Ian Campbell Apr 18 at 19:47

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