df <- data.frame(
  A_gsr =c("2.752,2.752,2.752,2.752,2.752,2.752,2.752,2.911,2.911,3.555",
           "2.999,2.999,2.999,2.752,2.752,2.752,2.752"),
  B_gsr = c("1.34,1.34,1.34,1.55,1.55,1.55,1.55,1.55,1.55,1.55",
            "1.56,1.56,1.56,1.55,1.55,1.55,1.55,NA,NA,NA,NA,1.34,1.34,1.34"),
  C_gsr = c("NA,NA,NA,0.147,0.147,0.147,0.147,0.147,NA",
            "0.146,0.146,0.146,0.146,0.146,0.146,0.146,0.146,0.146,0.146")
)
lapply(df[,1:3], function(x) gsub("\\b(\\d+\\.\\d+|NA)(?:,\\1)+\\b", "\\1", x))

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