compare values from consecutive rows in R

I have a datatable and for each datatable$Ppt and each datatable$nitem, when there is "fffword" in datatable$Region, I need to extract the value of "fffword" and compare it with the value of the following "word". If the two values are the same, then I need a value of 0 in datatable$Output, if the two values are different, I need a value of 1 in datatable$Output.

I have tried with:

 datatable %>% group_by(Ppt, nitem) %>%
   mutate(Output = ifelse(as.numeric(gsub("fffword([0-9]+).*","\\1",Region) == lag(as.numeric(gsub("word([0-9]+).*","\\1",Region)), 0L,ifelse(as.numeric(gsub("fffword([0-9]+).*","\\1",Region) != lag(as.numeric(gsub("word([0-9]+).*","\\1",Region)), 1L)

but it doesn't work.

 #Ppt      Region            nitem      Output
 #1        "fffword8"        93         0
 #1        "word8"           93         0
 #1        "fffword9"        93         1
 #1        "word2"           122        1
 #1        "fffword3"        122        0
 #1        "word3"           122        0
 #1        "word6"           122        1
 #1        "fffword7"        122        0
 #1        "word7"           122        0
 #1        "fffword8"        122        0
 #1        "word8"           122        0
 #54       "fffword8"        4          0
 #54       "word8"           4          0
 #54       "fffword9"        4          1
 #54       "word2"           4          1
 #54       "fffword2"        10         0
 #54       "word4"           10         0
 #54       "word6"           10         1
 #54       "fffword23"       10         0
 #54       "word23"          10         0
 #54       "fffword24"       5          0
 #54       "word24"          5          0