python - Read R function output as columns

Question

I'm trying to come up with a way to solve this question I asked yesterday:

rpy2 fails to import 'rgl' R package

My goal is to check if certain packages are installed inside R from within python.

Following the recommendation by Dirk Eddelbuettel given in a comment on his answer, I'm using the installed.packages() function from R to list all the available packages.

This is what I've got so far:

from rpy2.rinterface import RRuntimeError
from rpy2.robjects.packages import importr
utils = importr('utils')

def importr_tryhard(packname, contriburl):
    try:
        rpack = utils.installed_packages()
    except RRuntimeError:
        rpack = []
    return rpack

contriburl = 'http://cran.stat.ucla.edu/'
rpack = importr_tryhard(packname, contriburl)
print rpack

Which returns a quite large output of the form:

           Package      LibPath                         Version   
ks         "ks"         "/usr/local/lib/R/site-library" "1.8.13"  
misc3d     "misc3d"     "/usr/local/lib/R/site-library" "0.8-4"   
mvtnorm    "mvtnorm"    "/usr/local/lib/R/site-library" "0.9-9996"
rgl        "rgl"        "/usr/local/lib/R/site-library" "0.93.986"
base       "base"       "/usr/lib/R/library"            "3.0.1"   
boot       "boot"       "/usr/lib/R/library"            "1.3-9"   
class      "class"      "/usr/lib/R/library"            "7.3-9"   
cluster    "cluster"    "/usr/lib/R/library"            "1.14.4"  
codetools  "codetools"  "/usr/lib/R/library"            "0.2-8"   
compiler   "compiler"   "/usr/lib/R/library"            "3.0.1"   
datasets   "datasets"   "/usr/lib/R/library"            "3.0.1"   
foreign    "foreign"    "/usr/lib/R/library"            "0.8-49"  
graphics   "graphics"   "/usr/lib/R/library"            "3.0.1"   
grDevices  "grDevices"  "/usr/lib/R/library"            "3.0.1"   
grid       "grid"       "/usr/lib/R/library"            "3.0.1"   
KernSmooth "KernSmooth" "/usr/lib/R/library"            "2.23-10" 
lattice    "lattice"    "/usr/lib/R/library"            "0.20-23" 
MASS       "MASS"       "/usr/lib/R/library"            "7.3-29"  
Matrix     "Matrix"     "/usr/lib/R/library"            "1.0-14"  
methods    "methods"    "/usr/lib/R/library"            "3.0.1"   
mgcv       "mgcv"       "/usr/lib/R/library"            "1.7-26"  
nlme       "nlme"       "/usr/lib/R/library"            "3.1-111" 
nnet       "nnet"       "/usr/lib/R/library"            "7.3-7"   
parallel   "parallel"   "/usr/lib/R/library"            "3.0.1"   
rpart      "rpart"      "/usr/lib/R/library"            "4.1-3"   
spatial    "spatial"    "/usr/lib/R/library"            "7.3-6"   
splines    "splines"    "/usr/lib/R/library"            "3.0.1"   
stats      "stats"      "/usr/lib/R/library"            "3.0.1"   
stats4     "stats4"     "/usr/lib/R/library"            "3.0.1"   
survival   "survival"   "/usr/lib/R/library"            "2.37-4"  
tcltk      "tcltk"      "/usr/lib/R/library"            "3.0.1"   
tools      "tools"      "/usr/lib/R/library"            "3.0.1"   
utils      "utils"      "/usr/lib/R/library"            "3.0.1"   
           Priority     
ks         NA           
misc3d     NA           
mvtnorm    NA           
rgl        NA           
base       "base"       
boot       "recommended"
class      "recommended"
cluster    "recommended"
...

I need to extract just the names of the packages installed, so either the first or the second columns would be enough for me.

I've tried using np.loadtxt(), np.genfromtxt() and with open(rpack) as csvfile:, but none was able to give back a list/array where either the columns or the rows was correctly separated (they all failed with different errors actually).

How could I read this output in column form, or more to the point, extract the names of the installed packages in a list/array?

Answer 1

rpack in your case is an rpy2.robjects.vectors.Matrix object. Therefore you can simply use rpy2 class method .rx() to extract the column:

mylist = list(rpack.rx(True, 1))

Have a try.