GDC Data Download “How-To” Using R/RStudio

Updated: May 14, 2020

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The purpose of this ‘How-To’ is to demonstrate the use of the GDC Repository to access the next generation sequencing data from TCGA and TARGET projects.

The GCD is a central repository for a large and varied human cancer datasets, as well as some limited data from cell lines. It also contains the associated clinical data for these samples.

This can be a helpful source to download this data locally for a variety of uses ranging from example datasets to use when testing new code, to retrieving it for validation of results you’ve found.

This tutorial will demonstrate how to download the RNA-seq data from the TARGET Pediatric Cancer project as well as the clinical data. Of course, there are various options for downloading data from TCGA/TARGET ranging using the GCD command line tool, or from various other repositories FTP sites like Broad Firehouse, UCSC XENA browser, and using TARGET data matrix.


We will use the GenomicDataCommons Bioconductor package. It should be noted that there is an alternative package, TCGAbiolinks for only TCGA data, but will not be covered here.


#Orientation with Package

There are 4 main types of objects:

  1. projects()
  2. files()
  3. cases()
  4. annotations()

Each of these can be filtered and specific fields can be selected. Then piped (%>%) into results() or results_all() to get a manifest file, which is a list with each file/case ID and also associated metadata for the files.

First, check your connection to the database.


Second, take a look at the available number of projects, available files, and patient samples (cases).

available_fields('projects') %>% length()
available_fields('files') %>% length()
available_fields('cases') %>% length()
available_fields('annotations') %>% length()

Third, check out the different projects available, which include TCGA-MESO, TCGA-ACC, TARGET-NBL. Important Note: There is an argument for legacy data in the GDC repository. Legacy datasets are the original data, as it was released by TCGA. By default, the GDC package will download the newest Harmonized data which is being reprocessed bioinformatically identically and using GRCh38.

You can create an empty query to simply select the first 10 projects and their properties like primary tissue site, type of cancer, whether it is open access. It is 10 datasets by default, but would be less or more depending on any filters provided to projects() function.

pQuery = projects()
presults = pQuery %>% results() # or optionally results_all()


Examine the feild/columns of the files available for each project. These include file name, file type (eg BAM, csv), and data type (sequencing type).


files() %>% count() #without filters, and only 10 Cohorts has 358,679 files

You can also examine the patient samples (cases) and the type of information that is available for each sample - such as primary site (tissue) and case ID.

qcases = cases() #patient samples
qcases$fields #grep_fields(), field_picker() can be useful here
head(available_fields('cases')) #clinical data elements "columns"
qcases %>% count() #number of patient cases/samples

Directed Searches in GCD

You can find the total number of files of a specific type of file, project, and cases . Remember to use available_feilds(files()) to find your facet arguments (column/field names) to select the appropriate information to summarize. The aggregations() function will create a list of dataframes for each facet you select.

In this example, the res object will include a dataframe called “data_type” which will have a summary count of all Gene Expression Quantification, Aligned reads, somatic mutation, etc. files available in the GDC.

#Use available fields and grep fields to find the facets you want.

#Use aggregrate to summarize the total number of files for each facet.
res = files() %>%
  #Default is to set facets from default_fields()
          'cases.project.project_id')) %>%

res$cases.project.project_id$key  %>% .[order(.)]
res.projects <- projects() %>%
  facet(c("project_id")) %>%

# str(res.projects)
res.cases <- cases() %>%
  facet() %>% #Default is to set facets for all default fields.


Query GDC for Gene Expression Data from the TARGET Project

As it is, there isn’t a central website or very efficient method to determine what are the available field names for each file type, so it does require a bit of printing out and visually searching for the information you are looking for.


I will need the project ID (eg TCGA, TARGET), the sample IDs (UUIDs) from the “associated_entities” field. I will also need to parse all the default fields, analysis_types, and workflow_types.

The files() function call produces a list, which contains the specified filters and the fields you will want to download. It is of class GDCQuery.


desired_fields <-c("cases.project.project_id",default_fields('files'),grep_fields('files', "associated_entities"),  "analysis.analysis_type", "analysis.workflow_type", "analysis.workflow_version")
length(desired_fields) #54 fields

qfiles <- files(fields=desired_fields) %>%
  filter(~ type == 'gene_expression' &
           analysis.workflow_type == 'HTSeq - Counts' &
          (cases.project.project_id == "TARGET-AML" |
             cases.project.project_id == "TARGET-NBL" |
             cases.project.project_id == "TARGET-WT" |
             cases.project.project_id == "TARGET-CCSK" |
             cases.project.project_id == "TARGET-OS" |
             cases.project.project_id == "TARGET-RT"))

qfiles %>% count()

Create ID Map for Manifest, Clinical, and Expression Files

Now, you can query the GDC for the information in the fields in the qfiles object. The output of the results_all() function call will be long nested list. Again, you will need to do many print statements to really get a handle on the information you’ve now downloaded. Be aware you are not downloading any data files at this point. The query is for the file identifiers, associated sample identifiers, etc.

The items in the list output from results_all() can be a vector, which we will print out, and some nested lists.

res.expn <- results_all(x=qfiles)

# str(res.expn)

Printing out a few of the list items can help clarify what type of information you’ve just downloaded in the res.expn object.

You have a vector of file names, a vector of file_ids, and then a nested list of “associated_entities”. For example, you can see that the file_id for one is “1f51fa92-c89b-4974-988e-666846e14400”. Then the associated_entities named “1f51fa92-c89b-4974-988e-666846e14400” is a dataframe with 1 row and 4 columns. The associated_entities for this particular file_id, “1f51fa92-c89b-4974-988e-666846e14400”, contains the “entity_submitter_id” feild, which is the legacy case unique identifier and likely the one you will be most familiar with. It also contains the “case_id” field which is the hash



The “cases” fields - if used in results() contains much of the clinical data elements that are extracted through gdc_clinical() function used below.

#there are 2 Sample IDs associated with a single file.
#Filter these out, since they are suspect.
idx <- sapply(res.expn$associated_entities , nrow) %>% grep(2, .)
#check that these are the expected files/samples which more than 1 ID associated

# res.expn$associated_entities[idx]
# res.expn$cases[idx] <- res.expn[ !grepl("list|data.frame", sapply(res.expn, class)) ] %>% %>%
  slice(-idx) %>% #remove the multiple ID mapped files
  mutate(project.project_id=unlist(res.expn$cases[-idx])) %>%
  bind_cols(., bind_rows(res.expn$associated_entities[-idx])) #associated_entities was a list of data.frames, converted a single data.frame with bind_rows()

dim( #474

# write.csv(, "GCD_TARGET_Data_Manifest_AML_NBL_WT_RT.csv", row.names = FALSE)

Create a Download Manifest file

qfiles <- qfiles %>%
  filter(~ file_id %in% names(res.expn$associated_entities[-idx]) )

qfiles %>% count() #469
manifest_df = qfiles %>% manifest()
dim(manifest_df) #469

# write.table(manifest_df, "TARGET_Manifest_RNAseq_Counts.txt", row.names = FALSE, sep="\t", quote=FALSE)

Download the files

#Add the GDC Client to your R options
# options(gdc_client="/home/jlsmith3/scripts/opt/bin/gdc-client")
# gdc_client()
#Set your destination directory (be aware this downloads your current working directory, unless set otherwise)
gdc_set_cache(directory = "Expn_Data/")
#download step
# fnames = gdcdata(manifest_df$id,progress=FALSE,access_method = "api", use_cached = FALSE)


Check MD5 Sums

#check MD5 sums

Reorganize and Concatenate the Downloaded Files


NOTE: here i had to use some bash reprocessing

  1. mv all counts files to a directory called Expn_Data/ (remove the nested directories)
  2. gunzip *.gz (some were gzipped, some not… )

files <- dir(path=path, pattern="*.counts", recursive = TRUE) %>%
  paste0(path, .)

cated <- catExpnData(filenames = files,
                     cols=c(1,2), header = FALSE)
lapply(cated, dim)
all(lapply(cated$`1`, function(x) identical(x, cated$`1`[,1]))) #check order is identical for all genes columns
counts <- cated$`2` %>% %>%
  mutate(Genes=cated$`1`[,1]) %>% #genes in same order in all datasets.
  dplyr::select(Genes, everything())

head(counts[,1:10]) <- dplyr::select(, file_name, entity_submitter_id) %>%
  mutate_at(vars(file_name, entity_submitter_id), funs(gsub("-","\\.", .)))%>%
  mutate_at(vars(file_name), funs(gsub(".gz", "",. )))

fixNames.df <- data.frame(names= colnames(counts)[-1] %>% gsub("^X", "",.))  %>%
  left_join(.,, by=c("names"="file_name"))

#Finally, update the column names
colnames(counts)[-1] <- fixNames.df$entity_submitter_id

# write.csv(counts, "TARGET_NBL_AML_RT_WT_HTSeq_Counts.csv", row.names = FALSE)

Download Clinical Data

from GDC Database

cases() %>% filter(~ project.project_id == "TARGET-AML") %>% count() #988 patients

case_ids <- cases() %>%
  filter(~ project.project_id == "TARGET-AML") %>%

#download the clinical data per patient
clin_res = gdc_clinical(case_ids)

sapply(clin_res, dim) %>%

# sapply(clin_res, colnames)
# sapply(clin_res, head)
#Combine all Clinical Data into a Master File
full_clin = with(clin_res,
     main %>% #what is main here? not a function...
     left_join(demographic, by = "case_id") %>%
     left_join(exposures, by = "case_id") %>%
     left_join(diagnoses, by = "case_id"))

dim(full_clin) # 988  33

Precompiled Clinical Data Elements from Study Authors

qClin <- files() %>%
    filter(~ type == 'clinical_supplement' &
             (cases.project.project_id == "TARGET-AML"|
             cases.project.project_id == "TARGET-NBL" |
             cases.project.project_id == "TARGET-WT"  |
           cases.project.project_id == "TARGET-RT"))

# str(qClin)
qClin %>% count()
manifest.clin <- manifest(qClin)
gdc_set_cache(directory = "~/Documents/GitHub/RNAseq_Cancer_Biomarkers")

clinFile <- gdcdata(uuids = manifest.clin$id)

The downloaded data is each in thier own directories, with the file UUID as the directory name. Need to organize and move the Clinical Data so it is more easily usable.

system("ls -1")

#didn't work--- need to figure out how . Works in terminal directly
system("find . -type f -name '*.xlsx' -exec mv {} . \;")

#note this below works since there were NOT other directories except the file UUID dirs.
#Do not use this if you have others present (though non-empty directories will just result in an error)
system("for dir in $(ls -1d */); do rmdir $dir; done")

Session Information


Updated: May 14, 2020

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