#!/usr/bin/env Rscript
# based on https://www.biostars.org/p/84467/#84495
# source("https://bioconductor.org/biocLite.R")
# biocLite("GenomicRanges")
# biocLite("rtracklayer")
biocLite("Rsamtools")
library(GenomicRanges)
library(rtracklayer)
library(Rsamtools)

GFFfile = "Sp.gff"
FASTAfile = "Sp.faa"

#Load the annotation and reduce it
GFF <- import.gff(GFFfile, format="gff", feature.type="exon")
head(GFF)

grl <- reduce(split(GFF, elementMetadata(GFF)$ID))

reducedGFF <- unlist(grl, use.names=T)
elementMetadata(reducedGFF)$gene_name <- rep(names(grl), elementNROWS(grl))

#Open the fasta file
FASTA <- FaFile(FASTAfile)
open(FASTA)

#Add the GC numbers
elementMetadata(reducedGFF)$nGCs <- letterFrequency(getSeq(FASTA, reducedGFF), "GC")[,1]
elementMetadata(reducedGFF)$widths <- width(reducedGFF)

#Create a list of the ensembl_id/GC/length
calc_GC_length <- function(x) {
  nGCs = sum(elementMetadata(x)$nGCs)
  width = sum(elementMetadata(x)$widths)
  c(width, nGCs/width)
}
output <- t(sapply(split(reducedGFF, elementMetadata(reducedGFF)$gene_name), calc_GC_length))
colnames(output) <- c("Length", "GC")

write.table(output, file="GC_lengths.tsv", sep="\t")

The above script has produced the below output:

"Length"        "GC"
"sp0000001-mRNA-1:exon:204"     17      0.529411764705882
"sp0000001-mRNA-1:exon:205"     631     0.393026941362916
"sp0000001-mRNA-1:exon:206"     146     0.417808219178082
"sp0000001-mRNA-1:exon:207"     187     0.379679144385027
"sp0000001-mRNA-1:exon:208"     2046    0.389540566959922
"sp0000001-mRNA-1:exon:209"     20      0.45
"sp0000001-mRNA-1:exon:210"     4       0.5

Should be all sp0000001-mRNA-1:exon:xxx be summed up to produce sp0000001 because in the below gff3 file the id is Parent=sp0000001?

My GFF file looks like this:

lcl|ScwjSwM_3729        maker   gene    9131    15536   .       -       .       ID=sp0000001;Name=sp0000001
lcl|ScwjSwM_3729        maker   mRNA    9131    15536   .       -       .       ID=sp0000001-mRNA-1;Parent=sp0000001;Name=sp0000001-mRNA-1;_AED=0.28;_eAED=0.28;_QI=0|0|0|0.14|1|1|7|0|1016
lcl|ScwjSwM_3729        maker   exon    15533   15536   .       -       .       ID=sp0000001-mRNA-1:exon:210;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   exon    14631   14650   .       -       .       ID=sp0000001-mRNA-1:exon:209;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   exon    12563   14608   .       -       .       ID=sp0000001-mRNA-1:exon:208;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   exon    11160   11346   .       -       .       ID=sp0000001-mRNA-1:exon:207;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   exon    10840   10985   .       -       .       ID=sp0000001-mRNA-1:exon:206;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   exon    10109   10739   .       -       .       ID=sp0000001-mRNA-1:exon:205;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   exon    9131    9147    .       -       .       ID=sp0000001-mRNA-1:exon:204;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   CDS     15533   15536   .       -       0       ID=sp0000001-mRNA-1:cds;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   CDS     14631   14650   .       -       2       ID=sp0000001-mRNA-1:cds;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   CDS     12563   14608   .       -       0       ID=sp0000001-mRNA-1:cds;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   CDS     11160   11346   .       -       0       ID=sp0000001-mRNA-1:cds;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   CDS     10840   10985   .       -       2       ID=sp0000001-mRNA-1:cds;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   CDS     10109   10739   .       -       0       ID=sp0000001-mRNA-1:cds;Parent=sp0000001-mRNA-1
lcl|ScwjSwM_3729        maker   CDS     9131    9147    .       -       2       ID=sp0000001-mRNA-1:cds;Parent=sp0000001-mRNA-1

> #Load the annotation and reduce it
> GFF <- import.gff(GFFfile, format="gff", feature.type="exon")
> head(GFF)
GRanges object with 6 ranges and 6 metadata columns:
              seqnames         ranges strand |   source     type     score     phase                        ID
                 <Rle>      <IRanges>  <Rle> | <factor> <factor> <numeric> <integer>               <character>
  [1] lcl|ScwjSwM_3729 [15533, 15536]      - |    maker     exon      <NA>      <NA> sp0000001-mRNA-1:exon:210
  [2] lcl|ScwjSwM_3729 [14631, 14650]      - |    maker     exon      <NA>      <NA> sp0000001-mRNA-1:exon:209
  [3] lcl|ScwjSwM_3729 [12563, 14608]      - |    maker     exon      <NA>      <NA> sp0000001-mRNA-1:exon:208
  [4] lcl|ScwjSwM_3729 [11160, 11346]      - |    maker     exon      <NA>      <NA> sp0000001-mRNA-1:exon:207
  [5] lcl|ScwjSwM_3729 [10840, 10985]      - |    maker     exon      <NA>      <NA> sp0000001-mRNA-1:exon:206
  [6] lcl|ScwjSwM_3729 [10109, 10739]      - |    maker     exon      <NA>      <NA> sp0000001-mRNA-1:exon:205
                Parent
       <CharacterList>
  [1] sp0000001-mRNA-1
  [2] sp0000001-mRNA-1
  [3] sp0000001-mRNA-1
  [4] sp0000001-mRNA-1
  [5] sp0000001-mRNA-1
  [6] sp0000001-mRNA-1
  -------
  seqinfo: 4724 sequences from an unspecified genome; no seqlength

If the ids have to be merge then what would be the best way to do it?

Thank you in advance.