title: Adding a legend to ggplot linegraph of multiple dataframes in R
body: <p>I want to add a legend to a ggplot linegraph of multiple dataframes in R.
  I read in several .csv files (see below) to dataframes, then plot them in R using the following code:</p>
  
  <pre><code>ggplot(data=ridge_u_s_summary,aes(x = times,y=means))+
    geom_errorbar(data=ridge_u_s_summary,aes(ymin=means-sd,ymax=means+sd),colour="red")+
    geom_line(aes(y=means),colour="red")+
    geom_line(data = valley_u_s_summary,aes(x=times,y=means))+
    theme_classic()+
    geom_errorbar(data=valley_u_s_summary,aes(ymin=means-sd,ymax=means+sd))+
    geom_line(data = edge_u_s_summary,aes(x=times,y=means),colour="blue")+
    geom_errorbar(data=edge_u_s_summary,aes(ymin=means-sd,ymax=means+sd),colour="blue")+
    labs(x="Time",y="Temperature in understory during January to April")
  </code></pre>
  
  <p>In order to add a legend to this, I have tried</p>
  
  <pre><code>Habitat &lt;- c("Edge")
  ggplot(data=edge_u_summary,aes(x = times,y=means,color=Habitat))+
    geom_errorbar(data=edge_u_summary,aes(ymin=means-sd,ymax=means+sd),colour="red")+
    geom_line(aes(y=means),colour="red")+
    geom_line(data = ridge_u_summary,aes(x=times,y=means))+
    geom_errorbar(data=ridge_u_summary,aes(ymin=means-sd,ymax=means+sd))+
    geom_line(data = valley_u_summary,aes(x=times,y=means),colour="blue")+
    geom_errorbar(data=valley_u_summary,aes(ymin=means-sd,ymax=means+sd),colour="blue")+
    labs(x="Time",y="Temperature in understory all year")
  </code></pre>
  
  <p>This gets me almost what I want- except it changed the color of the plot for some reason, and when I attempt to add the other variables to the legend as R gives the error:</p>
  
  <pre><code>"Error: Aesthetics must be either length 1 or the same as the data (25): x, y, colour"
  </code></pre>
  
  <p>The data looks something like this:</p>
  
  <p>edge_u_summary:</p>
  
  <pre><code>"","times","means","sd"
  "1",1,23.8256278538813,1.08250700768145
  "12",2,23.1031294452347,1.24911533974507
  "19",3,23.4439617486339,1.1282693292488
  "20",4,22.7613086770982,1.36975338509067
  "21",5,23.2025956284153,1.20295088366619
  "22",6,22.5241109530583,1.44166092397246
  "23",7,23.1135422343324,1.26558498566579
  "24",8,23.2541963015647,1.47021441335091
  "25",9,25.1409536784741,1.58548666490834
  "2",10,26.7320085166785,2.59539671383782
  "3",11,27.6513358778626,2.5977168687079
  "4",12,28.586775106082,2.87211533419383
  "5",13,28.5709923664122,2.79577350516269
  "6",14,29.5764872521246,3.26115806616442
  "7",15,28.4104832104832,2.70542254623265
  "8",16,28.3307583274274,2.5157045864679
  "9",17,26.9131787175989,1.8371272211906
  "10",18,26.3352232459249,1.71211772244667
  "11",19,25.2531787175989,1.12498732015416
  "13",20,24.652728561304,1.24019473277585
  "14",21,24.4688591703057,0.99064927009491
  "15",22,23.9340425531915,1.16463318058244
  "16",23,24.0581058951965,0.987431147782684
  "17",24,23.4854609929078,1.19542300490208
  "18",25,23.6280334728033,0.977115814231141
  </code></pre>
  
  <p>ridge_u_summary:</p>
  
  <pre><code>"","times","means","sd"
  "1",1,23.5870433511934,0.937068380991415
  "12",2,23.0331950207469,1.1488061017937
  "19",3,23.3496395963479,1.02861071580118
  "20",4,22.682918395574,1.28095122645134
  "21",5,23.1064616862839,1.11960341933558
  "22",6,22.4135546334716,1.36699461456579
  "23",7,22.9523592814371,1.19411131617966
  "24",8,22.5736514522822,1.44525141078227
  "25",9,24.0131017964072,1.20022890842346
  "2",10,24.4016586040083,1.61518041063122
  "3",11,25.6837805462386,1.49361866061128
  "4",12,26.0852107809261,2.0335844646935
  "5",13,26.5968368080518,1.80035938711879
  "6",14,26.7841959972395,2.24353092250421
  "7",15,26.6535363222249,1.7733853965812
  "8",16,26.5494824016563,1.97883869059574
  "9",17,25.9478177458034,1.47079061322174
  "10",18,25.5847212663455,1.67334903054897
  "11",19,24.9841852651788,1.13952974451756
  "13",20,24.505099931082,1.34188808323866
  "14",21,24.3428365730742,0.964465091164753
  "15",22,23.8500345065562,1.1826679089188
  "16",23,23.9638415366146,0.934203639374674
  "17",24,23.4138716356108,1.13425784998453
  "18",25,23.7044528659403,0.977776310460964
  </code></pre>
  
  <p>Valley_u_summary:</p>
  
  <pre><code>"","times","means","sd"
  "1",1,23.8609523809524,0.941137931036436
  "12",2,23.6167464114833,1.36368015448422
  "19",3,23.6931023210199,1.09423013467475
  "20",4,23.2622807017544,1.40370217291909
  "21",5,23.444655116051,1.13978244673363
  "22",6,22.9831738437002,1.37794014701823
  "23",7,23.2909416748126,1.17933203457316
  "24",8,23.2392657621708,1.35015918020873
  "25",9,24.302705345502,1.07391752061927
  "2",10,24.8187699680511,1.39386829705572
  "3",11,25.7716009129442,1.36677999460727
  "4",12,26.1712689545092,1.97824543923682
  "5",13,26.5006523157208,1.62284855146781
  "6",14,26.6692430278884,2.08567545174535
  "7",15,26.502446183953,1.55882287684552
  "8",16,26.28759936407,1.72625533400646
  "9",17,25.8817558746736,1.24691066538137
  "10",18,25.5448412698413,1.45728060915926
  "11",19,25.1434910277325,1.08377131492575
  "13",20,24.8136616362192,1.32224607164181
  "14",21,24.6306135770235,1.00789058764099
  "15",22,24.3593328038125,1.32214170798361
  "16",23,24.2933093994778,1.02334054495071
  "17",24,23.9780778395552,1.34031144743681
  "18",25,24.1241503976862,1.16464232030193
  </code></pre>
  
  <p>The data appear scrambled due to a sorting artifact, but are okay.</p>