mapply r中的ifelse语句

Question

I am using mapply to find the sum of a range of indices for all cases:

score = mapply(function(x, y, z) sum(df[x, y:z]), seq_len(nrow(df)), df$index, df$index+10)

How can I add a ifelse statement to mapply so that it only applies the function if df$index >5, else the sum is 0?

Answer 1

This should probably work

mapply(function(x, y, z) if (y > 5) sum(df[x, y:z]) else 0, 
         seq_len(nrow(df)), df$index, df$index+10)

Or you could avoid if / else by multiplying by (y > 5) so index > 5 would be multiplied by 1 ( TRUE ) giving sum(df[x, y:z]) and index <= 5 would be multiplied by 0 ( FALSE ) giving 0.

mapply(function(x, y, z) sum(df[x, y:z]) * (y > 5), 
        seq_len(nrow(df)), df$index, df$index+10)

Answer 2

Just wrap ifelse and it should work

mapply(function(x, y, z) ifelse(y > 5, sum(df[x, y:z]), 0), 
             seq_len(nrow(df)), df$index, df$index+10)

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A better option would be pre-assign based on the 'index' value to 0 for those 'index' that are less than or equal to 5. Should be more efficient

i1 <- df$index > 5
score[!i1] <- 0
score[i1] <- mapply(function(x, y, z) sum(df[x, y:z]),
                     seq_len(nrow(df))[i1], df$index[i1], df$index[i1] + 10)