title: Create a sequence of values by group between a min and max interval using dplyr
body: <p>this is surely a basic question but couldn't find a way to solve.</p>
  
  <p>I need to create a sequence of values for a minimum (dds_min) to maximum (dds_max) per group (fs).
  This is my data:</p>
  
  <pre><code>fs &lt;- c("early", "late")
  dds_min &lt;-as.numeric(c("47.2", "40"))
  dds_max &lt;-as.numeric(c("122", "105"))
  dds_min.max &lt;-as.data.frame(cbind(fs,dds_min, dds_max))
  </code></pre>
  
  <p>And this is what I did....</p>
  
  <pre><code>dss_levels &lt;-dds_min.max %&gt;% 
                  group_by(fs) %&gt;% 
                  mutate(dds=seq(dds_min,dds_max,length.out=100))
  </code></pre>
  
  <p>I intended to create a new variable (dds), that has to be 100 length and start and end at different values depending on "fs". My expectation was to end with another dataframe (dss_levels) with two columns (fs and dds), 200 values on it. </p>
  
  <p>But I am getting this error.</p>
  
  <pre><code>Error: Column `dds` must be length 1 (the group size), not 100
  In addition: Warning messages:
  1: In Ops.factor(to, from) : ‘-’ not meaningful for factors
  2: In Ops.factor(from, seq_len(length.out - 2L) * by) :
    ‘+’ not meaningful for factors
  </code></pre>
  
  <p>Any help would be really appreciated. </p>
  
  <p>Thanks!</p>