How to plot only a part of a Posixct variable?

Question

I have a df with two variables. The first is a time counter that reaches 9min at a 1000Hz acquisition rate (so it’s huge 540 thousand lines). The second variable is an electrophysiological measurement in us (micro Siemens). Follow the first 20 lines below:

> dput(head(SC,20))

structure(list(time = c(0, 0.001, 0.002, 0.003, 0.004, 0.005, 
0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 
0.015, 0.016, 0.017, 0.018, 0.019), Conductance = c(0, 0, 0, 
0.01, 0.01, 0.02, 0.03, 0.04, 0.05, 0.07, 0.07, 0.08, 0.09, 0.09, 
0.09, 0.09, 0.1, 0.09, 0.09, 0.09)), row.names = c(NA, 20L), class = "data.frame")

I converted the variable "time" to a Posixct and need to plot on a graph. However, I do not want to plot the entire Time variable. Only part of it. I have no skill with Posixct and do not know how to edit the "xlim" of the chart.

require(lubridate)
SC$time <- as_datetime(SC$time)

> head(SC$time)
[1] "1970-01-01 00:00:00 UTC" "1970-01-01 00:00:00 UTC"
[3] "1970-01-01 00:00:00 UTC" "1970-01-01 00:00:00 UTC"
[5] "1970-01-01 00:00:00 UTC" "1970-01-01 00:00:00 UTC"

> tail(SC$time,10)
 [1] "1970-01-01 00:09:13 UTC" "1970-01-01 00:09:13 UTC"
 [3] "1970-01-01 00:09:13 UTC" "1970-01-01 00:09:13 UTC"
 [5] "1970-01-01 00:09:13 UTC" "1970-01-01 00:09:13 UTC"
 [7] "1970-01-01 00:09:13 UTC" "1970-01-01 00:09:13 UTC"
 [9] "1970-01-01 00:09:13 UTC" "1970-01-01 00:09:13 UTC"

I used the following code but it takes all the information, including the x-axis format does not look good pq includes HORA (which is not relevant):

pl <- ggplot(SC, aes(x = time, Conductance)) + geom_line()

How to adjust the x-axis for any desired time unit (window)? For example: only from 2.5 minutes to 6.5 minutes (5min window therefore).

Answer 1

Look, the graph that you sent the image is in minutes no? If it goes from 0 to 9 minutes the graph shows from 00:00 to 09:00, being minutes:seconds.

But anyway, if you want to make sure it’s for seconds or minutes, just use minute() dplyr package. Here I am using second() because the first 20 dice are all in the first minute.

But what I would do to get what you want would be to use the filter() package dplyr to select the data, make the graph and at the end change the scale if I didn’t find the automatic good.

library(ggplot2)
library(dplyr)
library(lubridate)

SC %>% 
  mutate(second = second(time)) %>% 
  filter(between(second,.005,.012)) %>% 
  ggplot(aes(second(time), Conductance)) + 
  geom_line() +
  scale_x_continuous(breaks = seq(.005, .012, by = .002))

Another option would be to do the operation on the chart. You can use xlim to choose the x region of the chart.

ggplot(SC, aes(second(time), Conductance)) + 
  geom_line() +
  xlim(c(.005,.012))

Or use coord_cartesian to zoom in on the region you want and then, if you need to, change the scale.

ggplot(SC, aes(second(time), Conductance)) + 
  geom_line() +
  coord_cartesian(xlim=c(.005,.012)) +
  scale_x_continuous(breaks = seq(.005, .012, by = .002))