continuous value supplied to discrete scale - r

Question

I am new to ggplot2. In fact, I only discovered it last week and I haven't quite figured out yet how to use aesthetics and scales etc. There is probably a very easy solution to my problem but I couldn't find a satisfying answer online.
Sorry for the size of the message, but all the data used is in the following script:
dados
Fres Vc Lu
1 466 30 10
2 416 30 10
3 465 30 10
4 416 30 10
5 464 30 10
6 416 30 10
7 476 30 10
8 412 30 10
9 468 30 10
10 410 30 10
11 470 30 10
12 407 30 10
13 468 30 10
14 412 30 10
15 469 30 10
16 414 30 10
17 469 30 10
18 412 30 10
19 467 30 10
20 409 30 10
21 469 30 10
22 415 30 10
23 471 30 10
24 420 30 10
25 469 30 10
26 416 30 10
27 464 30 10
28 409 30 10
29 465 30 10
30 412 30 10
31 464 30 10
32 409 30 10
33 466 30 10
34 417 30 10
35 466 30 10
36 417 30 10
37 464 30 10
38 414 30 10
39 466 30 10
40 415 30 10
41 585 30 94
42 234 30 94
43 589 30 94
44 231 30 94
45 585 30 94
46 223 30 94
47 586 30 94
48 223 30 94
49 572 30 94
50 233 30 94
51 585 30 94
52 233 30 94
53 589 30 94
54 234 30 94
55 598 30 94
56 237 30 94
57 605 30 94
58 237 30 94
59 586 30 94
60 233 30 94
61 588 30 94
62 227 30 94
63 585 30 94
64 230 30 94
65 586 30 94
66 230 30 94
67 591 30 94
68 237 30 94
69 586 30 94
70 234 30 94
71 592 30 94
72 237 30 94
73 595 30 94
74 236 30 94
75 600 30 94
76 227 30 94
77 592 30 94
78 237 30 94
79 592 30 94
80 240 30 94
81 468 30 10
82 408 30 10
83 471 30 10
84 405 30 10
85 475 30 10
86 403 30 10
87 470 30 10
88 409 30 10
89 478 30 10
90 405 30 10
91 474 30 10
92 403 30 10
93 472 30 10
94 402 30 10
95 478 30 10
96 408 30 10
97 477 30 10
98 406 30 10
99 473 30 10
100 406 30 10
101 474 30 10
102 406 30 10
103 477 30 10
104 411 30 10
105 480 30 10
106 413 30 10
107 479 30 10
108 408 30 10
109 476 30 10
110 406 30 10
111 476 30 10
112 404 30 10
113 472 30 10
114 407 30 10
115 474 30 10
116 411 30 10
117 473 30 10
118 415 30 10
119 479 30 10
120 409 30 10
121 578 30 94
122 370 30 94
123 570 30 94
124 378 30 94
125 575 30 94
126 367 30 94
127 579 30 94
128 371 30 94
129 576 30 94
130 362 30 94
131 579 30 94
132 372 30 94
133 588 30 94
134 375 30 94
135 586 30 94
136 372 30 94
137 589 30 94
138 378 30 94
139 587 30 94
140 375 30 94
141 578 30 94
142 368 30 94
143 575 30 94
144 375 30 94
145 574 30 94
146 376 30 94
147 575 30 94
148 367 30 94
149 580 30 94
150 382 30 94
151 583 30 94
152 368 30 94
153 591 30 94
154 386 30 94
155 595 30 94
156 379 30 94
157 593 30 94
158 384 30 94
159 607 30 94
160 399 30 94
161 760 30 122
162 625 30 122
163 746 30 122
164 612 30 122
165 762 30 122
166 625 30 122
167 783 30 122
168 637 30 122
169 778 30 122
170 640 30 122
171 778 30 122
172 638 30 122
173 791 30 122
174 638 30 122
175 782 30 122
176 635 30 122
177 792 30 122
178 640 30 122
179 783 30 122
180 637 30 122
181 774 30 122
182 622 30 122
183 777 30 122
184 618 30 122
185 777 30 122
186 622 30 122
187 765 30 122
188 623 30 122
189 769 30 122
190 625 30 122
191 775 30 122
192 622 30 122
193 777 30 122
194 628 30 122
195 769 30 122
196 620 30 122
197 778 30 122
198 623 30 122
199 788 30 122
200 634 30 122
201 457 40 38
202 416 40 38
203 460 40 38
204 438 40 38
205 465 40 38
206 441 40 38
207 467 40 38
208 442 40 38
209 473 40 38
210 452 40 38
211 469 40 38
212 446 40 38
213 478 40 38
214 450 40 38
215 476 40 38
216 454 40 38
217 479 40 38
218 452 40 38
219 480 40 38
220 450 40 38
221 481 40 38
222 443 40 38
223 476 40 38
224 447 40 38
225 472 40 38
226 450 40 38
227 479 40 38
228 449 40 38
229 478 40 38
230 455 40 38
231 478 40 38
232 457 40 38
233 481 40 38
234 447 40 38
235 504 40 38
236 452 40 38
237 472 40 38
238 447 40 38
239 472 40 38
240 451 40 38
241 622 40 66
242 377 40 66
243 619 40 66
244 378 40 66
245 622 40 66
246 369 40 66
247 616 40 66
248 374 40 66
249 619 40 66
250 374 40 66
251 616 40 66
252 374 40 66
253 621 40 66
254 375 40 66
255 618 40 66
256 397 40 66
257 633 40 66
258 406 40 66
259 652 40 66
260 412 40 66
261 652 40 66
262 419 40 66
263 658 40 66
264 423 40 66
265 659 40 66
266 409 40 66
267 650 40 66
268 405 40 66
269 653 40 66
270 405 40 66
271 652 40 66
272 403 40 66
273 656 40 66
274 408 40 66
275 644 40 66
276 406 40 66
277 649 40 66
278 412 40 66
279 650 40 66
280 406 40 66
281 853 40 122
282 330 40 122
283 859 40 122
284 323 40 122
285 842 40 122
286 308 40 122
287 842 40 122
288 324 40 122
289 831 40 122
290 334 40 122
291 838 40 122
292 341 40 122
293 836 40 122
294 328 40 122
295 840 40 122
296 324 40 122
297 836 40 122
298 321 40 122
299 831 40 122
300 328 40 122
301 833 40 122
302 328 40 122
303 840 40 122
304 330 40 122
305 831 40 122
306 321 40 122
307 833 40 122
308 328 40 122
309 833 40 122
310 321 40 122
311 840 40 122
312 319 40 122
313 838 40 122
314 317 40 122
315 831 40 122
316 319 40 122
317 827 40 122
318 323 40 122
319 836 40 122
320 328 40 122
321 442 40 38
322 407 40 38
323 437 40 38
324 410 40 38
325 444 40 38
326 412 40 38
327 440 40 38
328 414 40 38
329 439 40 38
330 413 40 38
331 436 40 38
332 416 40 38
333 446 40 38
334 412 40 38
335 438 40 38
336 414 40 38
337 443 40 38
338 408 40 38
339 446 40 38
340 407 40 38
341 445 40 38
342 413 40 38
343 453 40 38
344 414 40 38
345 449 40 38
346 417 40 38
347 447 40 38
348 411 40 38
349 443 40 38
350 417 40 38
351 447 40 38
352 410 40 38
353 449 40 38
354 409 40 38
355 442 40 38
356 413 40 38
357 451 40 38
358 412 40 38
359 447 40 38
360 420 40 38
361 526 40 66
362 467 40 66
363 532 40 66
364 470 40 66
365 528 40 66
366 474 40 66
367 529 40 66
368 472 40 66
369 533 40 66
370 480 40 66
371 542 40 66
372 487 40 66
373 545 40 66
374 504 40 66
375 549 40 66
376 507 40 66
377 546 40 66
378 517 40 66
379 541 40 66
380 518 40 66
381 554 40 66
382 514 40 66
383 564 40 66
384 514 40 66
385 571 40 66
386 522 40 66
387 575 40 66
388 525 40 66
389 582 40 66
390 533 40 66
391 588 40 66
392 536 40 66
393 591 40 66
394 553 40 66
395 592 40 66
396 557 40 66
397 592 40 66
398 563 40 66
399 583 40 66
400 568 40 66
> dadosc <- summarySE(dados, measurevar="Fres", groupvars=c("Vc","Lu"))
> dadosc
Vc Lu N Fres sd se ci
1 30 10 80 440.6875 30.91540 3.456447 6.879885
2 30 94 80 445.0250 150.97028 16.878990 33.596789
3 30 122 40 701.7000 75.06688 11.869115 24.007552
4 40 38 80 444.6125 23.31973 2.607225 5.189552
5 40 66 80 526.7125 90.77824 10.149316 20.201707
6 40 122 40 581.1250 259.74092 41.068645 83.069175
> ggplot(dadosc, aes(x=Lu, y=Fres, colour=Vc)) +
+ geom_errorbar(aes(ymin=Fres-se, ymax=Fres+se), width=5) +
+ geom_point()
> pd <- position_dodge(0.1)
Up to here I got this graph, very close to my desired graph, except for the fact I´d like a legend with only two colors, one for Vc=30 and other for Vc=40.
![enter image description here][1]
Then I try the following script:
ggplot(dadosc, aes(x=Lu, y=Fres, ymax = max(Fres), colour=Vc, group=Vc)) +
+ geom_errorbar(aes(ymin=Fres-se, ymax=Fres+se), colour="black", width=.1, position=pd) +
+ geom_point(position=pd, size=3, shape=21, fill="white") + # 21 is filled circle
+ xlab("Machining lenght (mm)") +
+ ylab("Machining forces (N)") +
+ scale_colour_hue(name="Cutting Velocity",
+ breaks=c("30", "40"),
+ labels=c("Vc = 30 m/min", " Vc = 40 m/min "),
+ l=40) +
+ ggtitle("The Effect of Cutting Velocity on Machining Forces") +
+ expand_limits(y=0) +
+ scale_y_continuous(breaks=0:750*50) +
+ theme_bw() +
+ theme(legend.justification=c(1,0),
+ legend.position=c(1,0))
Error: Continuous value supplied to discrete scale
And I receive this message:
"Error: Continuous value supplied to discrete scale"!

Answer 1

Vc should be a factor if you want two values in the legend. You were getting that error because you were trying to scale Vc as discrete (breaks = c(30, 40)) when it was of type integer
ggplot(dadosc, aes(x=Lu, y=Fres, colour=factor(Vc))) +
...