I solved the 1? problem with this command:
matrix2plot2[,"sensor_data"]<-as.numeric(as.character((matrix2plot2[,"sensor_data"])))
In fact before the previous command I if write:
str(matrix2plot2[,"sensor_data"])
I get:
Factor w/ 10 levels "131.22","148.532",..: 4 6 4 6 9 8 9 8 3 1 ...
And after the command
matrix2plot2[,"sensor_data"]<-as.numeric(as.character((matrix2plot2[,"sensor_data"])))
if I write:
str(matrix2plot2[,"sensor_data"])
I get:
num [1:16] 30.4 31.2 30.4 31.2 50.1 ...
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but I can't solve the 2? problem....