R tips and tricks

basic-data-analysis.R

########################################
# 1. Counting the discrete occurrences 
#    of a value in each column of a 
#    matrix. Store the count for each 
#    column in a new vector whose size
#    is the number of columns in the 
#    matrix. 
########################################
# make a 3x3 matrix with columns
# having 0, 1, and 2 zeros
#      [,1] [,2] [,3]
# [1,]    1    0    0
# [2,]    2    1    0
# [3,]    3    1    1
m = matrix(c(1,2,3,0,1,1,0,0,1), nrow=3)

# setup a vector whose size is equal to the
# the number of columns in m.
num_zeros = mat.or.vec(ncol(x), 1)

# for each column, count the number 
# of zeros and store the result in the 
# ith bucket in our num_zeros
# vector.
for (i in seq(1, ncol(m))) {
  num_zeros[i] = sum(m[,i]==0)
}