Loop FOR with histogram() from lattice

Hi all,

I'm encountering a problem I do not understand on my data:

library (lattice)

Mpool1 <- Table[Table$Subarea %in% c("52E9", "51E9"),]
Mpool2 <- Table[Table$Subarea %in% c("53F0", "52F0"),]
Mpool3 <- Table[Table$Subarea %in% c("51F0", "50F0"),]
Mpool4 <- Table[Table$Subarea %in% c("51F1", "52F1"),]

Mpool <- list(Mpool1, Mpool2, Mpool3, Mpool4)


histogram(~ Mpool[[2]]$LngtClas | Mpool[[2]]$SpCode, type = "count", col = "lightgrey", xlab= "LngtClas", main = paste("Length distribution per species for Mpool", "2", sep = "_"))

#### This part works perfectly and I obtain the graph reprensenting Mpool2 length class count per species.
#### Now when I want to automatize this with a "for" loop nothing is plotted.

for (i in c(2)){
windows()
histogram(~ Mpool[[i]]$LngtClas | Mpool[[i]]$SpCode, type = "count", col = "lightgrey", xlab= "LngtClas", main = paste("Length distribution per species for Mpool", i, sep = "_"))
print (i)
}

### Running this loop I obtained  windows filled grey (no plot drawn at all) but the print (i) print a "2" as expected. I really dont understand what's wrong with the loop. There is no error message and no notification in R. You can find enclosed my data in txt file.

Thank you very much for any help,

Xochitl C.

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Xochitl CORMON
+33 (0)3 21 99 56 84

Doctorante en sciences halieutiques
PhD student in fishery sciences

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IFREMER
Centre Manche Mer du Nord
150 quai Gambetta
62200 Boulogne-sur-Mer

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<Table.txt>