Counting the NA's in a part of a row in data.table

问题

I have a dataset df of which the structure looks similar to the example below:

nr countrycode questionA questionB questionC WeightquestionA WeightquestionB WeightquestionC
1  NLD               2         1         4         0.6             0.2             0.2
2  NLD               NA        4         NA        0.4             0.4             0.2
3  NLD               4         4         1         0.2             0.2             0.6
4  BLG               1         NA        1         0.1             0.5             0.4
5  BLG               5         3         5         0.2             0.2             0.6

The questions A, B and C relate to a similar topic and as a result I would like to create an average score for all questions, taking into account the importance of each question (WeightquestionA WeightquestionB WeightquestionC).

Currently I have manually calculated the average score.

(questionA*WeightquestionA) + (questionB*WeightquestionB) + (questionC*WeightquestionC)

This would not be an insurmountable problem were it not for the NA's (for which: no they cannot be removed). As a result I would like to automate the process.

I am currently thinking of using sum(!is.na()) for counting the non-NA's in each question (A,B,C) for each row (1 through 5) and putting that value into a new column.

With data.table I however always have trouble getting the syntax right. I believe it should be something like:

df[, NonNA:=sum(!is.na(questionA + questionB + questionC))]

But this sums all NA's in the column, instead of for each row. How should I write the syntax to calculate per row?

I would like to refer to the columns separately by name, because they are not next to each other in the actual df.

Desired output:

nr countrycode qA qB qC WeightquestionA WeightquestionB WeightquestionC NonNA
1  NLD         2  1  4         0.6             0.2             0.2      3
2  NLD         NA 4  NA        0.4             0.4             0.2      1
3  NLD         4  4  1         0.2             0.2             0.6      3
4  BLG         1  NA 1         0.1             0.5             0.4      2
5  BLG         5  3  5         0.2             0.2             0.6      3

回答1:

Using data.table, this you could do this:

df[, NonNA := sum(!is.na(questionA), !is.na(questionB), !is.na(questionC)), by = .(nr)]

A base solution:

df$nonNA <- rowSums(!is.na(df[,c("questionA", "questionB", "questionC")]))

回答2:

Another alternative with recommendation from snoram:

df[, NonNA := rowSums(!is.na(.SD)), 
    .SDcols=paste0("question", LETTERS[1:3])]

And also:

df[, NonNA := Reduce(function(x, y) x + !is.na(y), .SD, init=rep(0L, .N)), 
    .SDcols=paste0("question", LETTERS[1:3])]

回答3:

We can count non NA (for column questionA,questionB and questionC i.e. column number 3 to 5) using apply as below:

df$nonNA=apply(df[,3:5], 1, function(x) length(which(!is.na(x))))

or (suggestion from snoarm)

df$nonNA=apply(df[,3:5], 1, function(x) sum(!is.na(x)))

Sample output:

   questionA questionB questionC nonNA
1         2         1         4     3
2        NA         4        NA     1
3         4         4         1     3
4         1        NA         1     2
5         5         3         5     3

来源：https://stackoverflow.com/questions/52513666/counting-the-nas-in-a-part-of-a-row-in-data-table

标签

sum

data.table