query <- GDCquery(project = "TCGA-BRCA",

                  data.category = "Transcriptome Profiling",

                  data.type = "miRNA Expression Quantification", 

                  workflow.type = "BCGSC miRNA Profiling"

barcode = TNBC_barcode)

GDCdownload(query,method='api',files.per.chunk = 50)

BRC_DATA1 <- GDCprepare(query)####一般到GDCprepare就齐活了

library(SummarizedExperiment)

BRC_TNBC =assay(BRC_DATA1)

报错：Error in (function (classes, fdef, mtable)  : 

  unable to find an inherited method for function ‘assay’ for signature ‘"data.frame", "missing"’