title: Remove columns of dataframe based on conditions in R
body: <p>I have to remove columns in my dataframe which has over 4000 columns and 180 rows.The conditions I want to set in to remove the column in the dataframe are:
  (i) Remove the column if there are less then two values/entries in that column
  (ii) Remove the column if there are no two consecutive(one after the other) 
  values in the column.
  (iii) Remove the column having all values as NA.
  I have provided with conditions on which a column is to be deleted. The aim here is not just to find a column by its name like in "How do you delete a column in data.table?". 
  I Illustrate as follows:</p>
  
  <pre><code>A       B    C   D  E
  0.018  NA    NA  NA NA
  0.017  NA    NA  NA NA
  0.019  NA    NA  NA NA
  0.018  0.034 NA  NA NA
  0.018  NA    NA  NA NA
  0.015  NA    NA  NA 0.037
  0.016  NA    NA  NA 0.031
  0.019  NA    0.4 NA 0.025
  0.016  0.03  NA  NA 0.035
  0.018  NA    NA  NA 0.035
  0.017  NA    NA  NA 0.043
  0.023  NA    NA  NA 0.040
  0.022  NA    NA  NA 0.042
  </code></pre>
  
  <p>Desired dataframe:</p>
  
  <pre><code>A       E
  0.018   NA
  0.017   NA
  0.019   NA
  0.018   NA
  0.018   NA
  0.015   0.037
  0.016   0.031
  0.019   0.025
  0.016   0.035
  0.018   0.035
  0.017   0.043
  0.023   0.040
  0.022   0.042
  </code></pre>
  
  <p>How can I incoporate these three conditions in one code. I would appreciate your help in this regard.
  Reproducible example</p>
  
  <pre><code>structure(list(Month = c("Jan-2000", "Feb-2000", "Mar-2000", 
  "Apr-2000", "May-2000", "Jun-2000"), A.G.L.SJ.INVS...LON..DEAD...13.08.15 = c(NA_real_, 
  NA_real_, NA_real_, NA_real_, NA_real_, NA_real_), ABACUS.GROUP.DEAD...18.02.09 = c(0.00829384766220866, 
  0.00332213653674028, 0, 0, NA, NA), ABB.R..IRS. = c(NA_real_, 
  NA_real_, NA_real_, NA_real_, NA_real_, NA_real_)), .Names = c("Month", 
  "A.G.L.SJ.INVS...LON..DEAD...13.08.15", "ABACUS.GROUP.DEAD...18.02.09", 
  "ABB.R..IRS."), class = c("data.table", "data.frame"), row.names = c(NA, 
  -6L), .internal.selfref = &lt;pointer: 0x0000000001c90788&gt;)
  </code></pre>