Question

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how to define fill colours in ggplot histogram?

I want to plot (histogram) counts of fishes per length class from a data frame which summarize this information in a binned format (data.frame(…,length=length, counts=N)). I’m a new user of ggplot2, but seems It could be a good choice. Can I create this histogram from a data.frame object?

Sorry for being so brief, Here is the structure of a piece of df,

'data.frame':   416 obs. of  3 variables:
 $ specie: Factor w/ 1 level "speciesA": 1 1 1 1 1 1 1 1 1 1 ...
 $ length: num  34.5 35 35.5 36 36.5 37 37.5 38 38.5 39 ...
 $ Counts: num  2 0 0 0 1 0 1 1 0 1 ...

In this case, fishers catch 2 individuals 34.5 cm large, 1 36.5, and so on…
Thank you very much for your answers

Answer 1

Since you did not provide a sample of your data, I have created data per your description.

Length of fishes from 34.5 to 49.5 (arbitrary units: a.u.). Min length of fishes was 34.5 and Max length of fishes was 49.5

 x <- 34.5:49.5

Number of fishes having a specific length starts at 0 and ends at 2.

 y <- 0:2

Create a sample of counts having the length of x

 Counts <- sample(y, length(x), replace=TRUE)

Create a dataframe1 that includes length and counts. Notice: The structure of df1 satisfies the data structure per your description

df1 <- data.frame(length=x, Counts = Counts)

Since you already counted the number of fishes having a specific length, you have to convert it back to the original format, i.e., if 2 fishes having 34.5(a.u), it should be converted back to two 34.5s.

df2 <- data.frame(length = rep(df1$length, df1$Counts))

Plot the data using ggplot function. Notice there are many ways to do the same plot. You may try geom_histogram to get the same plot as well.

require("ggplot2")
ggplot(data=df2, aes(x=length, xmin=34.5, xmax=49.5)) + stat_bin(binwidth=1)

Check this site for more info

Hope this helps!