title: Extracting individuals with Plink. Error: Line 1 of --keep file has fewer tokens than expected
body: <p>I have files with the 2504 individuals of the 1000 genomes project, and I want to filter by population. I did the following for the first population (ACB): </p>
  
  <pre><code>plink --file all1000gen --keep indACB.txt --make-bed --out all1000genACB
  </code></pre>
  
  <p>but it gives back the following error:</p>
  
  <pre><code>Error: Line 1 of --keep file has fewer tokens than expected.
  </code></pre>
  
  <p>my indACB.txt file looks like this:</p>
  
  <pre><code>head indACB.txt 
  HG01879
  HG01880
  HG01882
  HG01883
  HG01885
  HG01886
  HG01889
  HG01890
  HG01894
  HG01896
  </code></pre>
  
  <p>which I made (por each population, using grep) from the population information file that's available in the 1000 genomes page, which has a two times the individual ID (first two columns) and one with the population name, as shown:</p>
  
  <pre><code>head indpop2.txt
  HG00096 HG00096 GBR
  HG00097 HG00097 GBR
  HG00099 HG00099 GBR
  HG00100 HG00100 GBR
  HG00101 HG00101 GBR
  HG00102 HG00102 GBR
  HG00103 HG00103 GBR
  HG00105 HG00105 GBR
  HG00106 HG00106 GBR
  HG00107 HG00107 GBR
  </code></pre>
  
  <p>I think there's a problem with my --keep file, but I'm not sure what's the wanted structure of the txt file. </p>
  
  <p>I also tried greping ACB individuals from indpop2.txt , so the new indACB.txt file looks like this:</p>
  
  <pre><code>head indACB2.txt 
  HG01879 HG01879 ACB
  HG01880 HG01880 ACB
  HG01882 HG01882 ACB
  HG01883 HG01883 ACB
  HG01885 HG01885 ACB
  HG01886 HG01886 ACB
  HG01889 HG01889 ACB
  HG01890 HG01890 ACB
  HG01894 HG01894 ACB
  HG01896 HG01896 ACB
  </code></pre>
  
  <p>But it yields the following error:</p>
  
  <pre><code>plink --file allconcat39 --keep indACB2.txt --make-bed --out allconcat43ACB
  
  Error: No people remaining after --keep.
  </code></pre>