Hello everyone, I am struggling to get an FPKM matrix using countToFPKM library. everything seems running here is my script I get error.

    library("devtools")
    library("biomaRt")
    library("dplyr")
    library(countToFPKM)

    file.readcounts<- as.matrix(read.csv("Matrix.csv", header = TRUE, row.names = 1))
    nrow(file.readcounts)
    ens_build = "sep2015"
    dataset="hsapiens_gene_ensembl"
    mart <- useEnsembl(biomart = "ENSEMBL_MART_ENSEMBL", dataset = dataset, version = 80)

   gene.annotations <- biomaRt::getBM(mart = mart, attributes=c("ensembl_gene_id", "external_gene_name",
                                                             "start_position", "end_position"))
  gene.annotations <- dplyr::transmute(gene.annotations, external_gene_name,  ensembl_gene_id, length = end_position - start_position)
  convert order column in gene.annotation and make first column as row.name
   # Filter and re-order gene.annotations to match the order in feature counts matrix
   gene.annotations <- gene.annotations %>% dplyr::filter(gene.annotations$ensembl_gene_id %in% row.names(file.readcounts))
    gene.annotations <- gene.annotations[order(match(gene.annotations$ensembl_gene_id, rownames(file.readcounts))),]
    # Assign feature lenghts into a numeric vector.
    featureLength <- gene.annotations$length

the future length seems to be ok as integer value but at the end here is the error

fpkm_matrix <- fpkm (file.readcounts, featureLength=featureLength, meanFragmentLength=NULL)

Error in fpkm(file.readcounts, featureLength = featureLength, meanFragmentLength = NULL) : 
length(featureLength) == nrow(counts) is not TRUE

I can't understand the error the match function seems working fine...

I accept any help, thank you

You are pulling gene length out of biomart? Why would you do that? Why do you think intron length matters?