How to count the number of occurrences of a given value for each row?-CodePudding

I'm sure this is a really easy fix but I can't seem to find the answer... I am trying to create a column at the end of my dataframe that is a sum of the number of times a specific value (say "1") appears across that row. So for example, if I started with the following dataframe:

Data:

X1 <- c(5,1,7,8,1,5)
X2 <- c(5,0,0,2,3,7)
X3 <- c(6,2,3,4,1,7)
X4 <- c(1,1,5,2,1,7)

df <- data.frame(id,X1,X2,X3,X4)

  id X1 X2 X3 X4
1  1  5  5  6  1
2  2  1  0  1  1
3  3  7  0  3  5
4  4  8  2  4  2
5  5  1  3  2  1
6  6  5  7  7  7

and I was trying to identify how many times the value "1" appears across that row, I would want the output to look like this:

  id X1 X2 X3 X4 one_appears
1  1  5  5  6  1           2
2  2  1  0  1  1           3
3  3  7  0  3  5           0
4  4  8  2  4  2           0
5  5  1  3  2  1           2
6  6  5  7  7  7           0

Thanks very much in advance!

CodePudding user response：

We can use rowSums on a logical matrix

df$one_appears <- rowSums(df == 1, na.rm = TRUE)

-output

> df
  id X1 X2 X3 X4 one_appears
1  1  5  5  6  1           2
2  2  1  0  1  1           3
3  3  7  0  3  5           0
4  4  8  2  4  2           0
5  5  1  3  2  1           2
6  6  5  7  7  7           0

CodePudding user response：

df %>% 
  mutate(
    one = rowSums(across(everything(), ~ .x == 1))
  )

# A tibble: 6 × 6
     id    X1    X2    X3    X4   one
  <int> <dbl> <dbl> <dbl> <dbl> <dbl>
1     1     5     5     6     1     2
2     2     1     0     2     1     2
3     3     7     0     3     5     0
4     4     8     2     4     2     0
5     5     1     3     1     1     3
6     6     5     7     7     7     0

CodePudding user response：

Another option using apply with sum:

id <- c(1:6)
X1 <- c(5,1,7,8,1,5)
X2 <- c(5,0,0,2,3,7)
X3 <- c(6,2,3,4,1,7)
X4 <- c(1,1,5,2,1,7)

df <- data.frame(id,X1,X2,X3,X4)
df$one_appear = apply(df, 1, \(x) sum(x == 1))
df
#>   id X1 X2 X3 X4 one_appear
#> 1  1  5  5  6  1          2
#> 2  2  1  0  2  1          2
#> 3  3  7  0  3  5          0
#> 4  4  8  2  4  2          0
#> 5  5  1  3  1  1          3
#> 6  6  5  7  7  7          0

^{Created on 2023-01-18 with reprex v2.0.2}